Обсуждение: The case of PostgreSQL on NFS Server (II)
However, I'm newbie in PostgreSQL and would need some help from experts on two aspects. I apologize if these were already implicitely mentioned in the thread above.
My situation is the following:
1-running postgresql-9.2 server under my Ubuntu 12.04 LTS desktop,
2-user postgres created on the system,
3-two databases with several tables created, populated and owned by postgres,
4-these databases can be queried (SELECT, INSERT, etc.) by any system user of my desktop.
Now here are my two questions:
a) how can I know where my two databases are stored (I presume in a directory somewhere in my desktop path)?
b) this is the though one (at least for me ;) For data size reasons, I want to store my two databases in a NAS which I have mounted via NFS, but still keeping the postgresql server on my desktop.
I've seen in this message of the thread above, that NFS noac mounting option is highly recommended.
Apart from this, I don't see how to migrate the databases from my desktop directory determined in a) to my NAS. Could someone please provide the steps to accomplish that?
Apart from this, I don't see how to migrate the databases from my desktop directory determined in a) to my NAS. Could someone please provide the steps to accomplish that?
Thanks so much in advance,
--
Octavi Fors
I don't see how to migrate the databases from my desktop directory determined in a) to my NAS. Could someone please provide the steps to accomplish that?
ALTER DATABASE name SET TABLESPACE new_tablespace
You are solely responsible for any future frustration or harm you experience for choosing to access your data over NFS.
David J.
On Thu, Apr 2, 2015 at 3:01 PM, Octavi Fors <octavi@live.unc.edu> wrote: > Hi, > > this is somehow overlapping one thread which was already posted in this list >here. > > However, I'm newbie in PostgreSQL and would need some help from experts on > two aspects. I apologize if these were already implicitely mentioned in the > thread above. > > My situation is the following: > 1-running postgresql-9.2 server under my Ubuntu 12.04 LTS desktop, I'm running release 9.4 on Fedora 21, but hopefully what I can test will be of some use to you. > 2-user postgres created on the system, Good. > 3-two databases with several tables created, populated and owned by > postgres, > 4-these databases can be queried (SELECT, INSERT, etc.) by any system user > of my desktop. > > Now here are my two questions: > > a) how can I know where my two databases are stored (I presume in a > directory somewhere in my desktop path)? You might want to read: https://help.ubuntu.com/community/PostgreSQL They will be stored in the default location. On Fedora, this is /var/lib/pgsql/data. I don't know what it is on Ubuntu, but you can find out by using psql. Perhaps something like: sudo su - postgres -c 'SHOW data_directory;' Just using my normal id on Fedora, which is a PostgreSQL (not UNIX) super user, I can see: tsh009=# SHOW data_directory; data_directory --------------------- /var/lib/pgsql/data (1 row) tsh009=# > > b) this is the though one (at least for me ;) For data size reasons, I want > to store my two databases in a NAS which I have mounted via NFS, but still > keeping the postgresql server on my desktop. Well, if you insist. But I would not move the default data there. I'd keep it local. See below for an alternative. > I've seen in this message of the thread above, that NFS noac mounting option > is highly recommended. > Apart from this, I don't see how to migrate the databases from my desktop > directory determined in a) to my NAS. Could someone please provide the steps > to accomplish that? Well, there are a couple of approaches. Both will require UNIX root to accomplish. If you are running SELinux enabled & enforcing, it is even more complicated. But basically create an new, empty subdirectory on your NAS box. Look at the owner & group on the directory shown above (/var/lib/pgsql/data) and make it the new directory have the same information. Something like: sudo mkdir -p /NAS-box/pgsql-data sudo chown --reference /var/lib/pgsql/data /NAS-box/pgsql-data This sets up the new NAS-box/pgsql-data directory and assigns it the proper owner:group for use by the server. === Moving the data - BAD IDEA, IMO == #stop the postgresql server on your system, however you do that. I don't know Ubuntu. sudo cp -a /var/lib/pgsql/data/* /NAS-box/pgsql-data sudo cp -a /var/lib/pgsql/data/.* /NAS-box/pgsql-data sudo mount --bind /var/lib/pgsql/data /NAS-box/pgsql-data sudo restorecon -R /var/lib/pgsql/data # restore SELinux attributes Commands #1 and #2 copy all the data to the new directory. Command #3 does a "bind" mount so that any reference to /var/lib/pgsql/data is redirected to /NAS-box/pgsql Command #4 is if you run with SELinux. Update your fstab to maintain the bind mount when you reboot. The entry will look something like: /NAS-box/pgsql-data /var/lib/pgsql/data none bind === THE ABOVE IS A BAD IDEA === === Decent idea: === Create the NAS directory as above. Do _NOT_ copy anything into it! In psql, as a postgres super user, create a new TABLESPACE ref: http://www.postgresql.org/docs/9.2/interactive/sql-createtablespace.html CREATE TABLESPACE onNAS LOCATION '/NAS-box/pgsql-data'; CREATE DATABASE somedb TABLESPACE onNAS; \c somedb --connect to new database stored on the NAS CREATE TABLE sometable ... ; Now all the stuff in the "somedb" data base will reside on your NAS box. Now all you need worry about is that it is reliable and fast enough. Hopefully on at least a 1Gb ethernet. In this case, I don't know the SELinux commands to set the SELinux attributes. It is complicated. === Opinion. I have a NAS box. But I would worry about responsiveness. What is better, IMO, is an external SATA connected DAS box. DAS is "Direct Attached Storage". Many PCs have a eSATA port on the back side. You connect your DAS box to that will an eSATA cable. Now you have an external disk expansion which runs at full SATA speed, just like an internal disk drive. It's just an alternative. But you'd do the same thing as with the NAS to get data onto it. Well, except that you could dedicate an entire filesystem on the DAS to the /var/lib/pgsql/data with something like: # /dev/sd?n is the value for the DAS box. sudo mkfs.ext4 /dev/sd?n #create new filesystem on DAS sudo mount /dev/sd?n /tmp #mount it sudo cp -a /var/lib/pgsql/data/* /tmp sudo cp -a /var/lib/pgsql/data/.* /tmp sudo umount /tmp sudo mount /dev/sd?n /var/lib/pgsql/data #mount it sudo restorecon -R /var/lib/pgsql/data # update SELinux attributes The restorecon is only needed if you run SELinux > > > Thanks so much in advance, > > -- > Octavi Fors > -- If you sent twitter messages while exploring, are you on a textpedition? He's about as useful as a wax frying pan. 10 to the 12th power microphones = 1 Megaphone Maranatha! <>< John McKown
Thanks John for your extensive and helpful response.
If you are running SELinux enabled & enforcing, it is even
more complicated.
-no, I'm not running SELinux.
-My NAS is a Synology DS2415+ . I created a volume of ~72.44Tb with 12 8Tb Seagate ST8000AS0002 drives, with no encryption and Synology Hybrid RAID-2 (SHR) protection.
-Yes, the NAS is accessible only from two computers in the same Gigabit LAN. Actually, I have defined trunks on the router for speeding up the computers<->NAS access.
-The rest of the LAN has ~4 tcp/ip devices with very low traffic.
I have a NAS box. But I would worry about responsiveness. What is
better, IMO, is an external SATA connected DAS box. DAS is "Direct
Attached Storage". Many PCs have a eSATA port on the back side.
as far as I understand eSATA is not an option for me. First because I already have bought the DS2415+ NAS, which does not has eSATA I/O :(
And second, because I need the database to be accessible from two computers in the same LAN.
And second, because I need the database to be accessible from two computers in the same LAN.
See below the results to your comments/commands:
Just using my normal id on Fedora, which is a PostgreSQL (not UNIX)
super user, I can see:
tsh009=# SHOW data_directory;
data_directory
---------------------
/var/lib/pgsql/data
postgres@ev1:~$ psql -c 'SHOW data_directory;'
data_directory
------------------------------
/var/lib/postgresql/9.2/main
Note that inside /var/lib/postgresql/9.2/main directory there are the following files and subdirs:
postgres@ev1:~/9.2/main$ cd /var/lib/postgresql/9.2/main
postgres@ev1:~/9.2/main$ ls -ltr
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_snapshots
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_serial
-rw------- 1 postgres postgres 4 Aug 27 2014 PG_VERSION
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_twophase
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_tblspc
drwx------ 4 postgres postgres 4096 Aug 27 2014 pg_multixact
drwx------ 2 postgres postgres 4096 Sep 3 2014 pg_clog
drwx------ 2 postgres postgres 4096 Sep 3 2014 pg_subtrans
drwx------ 7 postgres postgres 4096 Sep 3 2014 base
-rw------- 1 postgres postgres 93 Mar 9 20:10 postmaster.pid
-rw------- 1 postgres postgres 133 Mar 9 20:10 postmaster.opts
drwx------ 2 postgres postgres 4096 Mar 9 20:10 pg_notify
drwx------ 2 postgres postgres 4096 Mar 9 20:11 global
drwx------ 3 postgres postgres 4096 Mar 27 13:57 pg_xlog
drwx------ 2 postgres postgres 4096 Apr 2 17:35 pg_stat_tmp
postgres@ev1:~/9.2/main$ du -sh ./*
postgres@ev1:~/9.2/main$ cd /var/lib/postgresql/9.2/main
postgres@ev1:~/9.2/main$ ls -ltr
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_snapshots
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_serial
-rw------- 1 postgres postgres 4 Aug 27 2014 PG_VERSION
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_twophase
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_tblspc
drwx------ 4 postgres postgres 4096 Aug 27 2014 pg_multixact
drwx------ 2 postgres postgres 4096 Sep 3 2014 pg_clog
drwx------ 2 postgres postgres 4096 Sep 3 2014 pg_subtrans
drwx------ 7 postgres postgres 4096 Sep 3 2014 base
-rw------- 1 postgres postgres 93 Mar 9 20:10 postmaster.pid
-rw------- 1 postgres postgres 133 Mar 9 20:10 postmaster.opts
drwx------ 2 postgres postgres 4096 Mar 9 20:10 pg_notify
drwx------ 2 postgres postgres 4096 Mar 9 20:11 global
drwx------ 3 postgres postgres 4096 Mar 27 13:57 pg_xlog
drwx------ 2 postgres postgres 4096 Apr 2 17:35 pg_stat_tmp
postgres@ev1:~/9.2/main$ du -sh ./*
485M ./base
448K ./global
624K ./pg_clog
28K ./pg_multixact
12K ./pg_notify
4.0K ./pg_serial
4.0K ./pg_snapshots
32K ./pg_stat_tmp
176K ./pg_subtrans
4.0K ./pg_tblspc
4.0K ./pg_twophase
4.0K ./PG_VERSION
129M ./pg_xlog
4.0K ./postmaster.opts
4.0K ./postmaster.pid
ofors@ev1:~$ sudo /etc/init.d/postgresql stop
* Stopping PostgreSQL 9.2 database server [ OK ]
ofors@ev1:~$ sudo mkdir -p /home/ofors/Documents/nas/
ofors@ev1:~$ sudo chown --reference /var/lib/postgresql/9.2/main /home/ofors/Documents/nas/pgsql-data
ofors@ev1:~$ sudo /etc/init.d/postgresql start
* Starting PostgreSQL 9.2 database server [ OK ]
postgres@ev1:~/9.2/main$ psql
psql (9.3.6, server 9.2.10)
Type "help" for help.
postgres=# CREATE TABLESPACE onNAS LOCATION '/home/ofors/Documents/nas/pgsql-data';
CREATE TABLESPACE
postgres=# ALTER DATABASE catalogs SET TABLESPACE onNAS;
ALTER DATABASE
You see that I used the ALTER from David in last message, instead your suggestion of creating the whole database again.
448K ./global
624K ./pg_clog
28K ./pg_multixact
12K ./pg_notify
4.0K ./pg_serial
4.0K ./pg_snapshots
32K ./pg_stat_tmp
176K ./pg_subtrans
4.0K ./pg_tblspc
4.0K ./pg_twophase
4.0K ./PG_VERSION
129M ./pg_xlog
4.0K ./postmaster.opts
4.0K ./postmaster.pid
ofors@ev1:~$ sudo /etc/init.d/postgresql stop
* Stopping PostgreSQL 9.2 database server [ OK ]
ofors@ev1:~$ sudo mkdir -p /home/ofors/Documents/nas/
ofors@ev1:~$ sudo chown --reference /var/lib/postgresql/9.2/main /home/ofors/Documents/nas/pgsql-data
ofors@ev1:~$ sudo /etc/init.d/postgresql start
* Starting PostgreSQL 9.2 database server [ OK ]
postgres@ev1:~/9.2/main$ psql
psql (9.3.6, server 9.2.10)
Type "help" for help.
postgres=# CREATE TABLESPACE onNAS LOCATION '/home/ofors/Documents/nas/pgsql-data';
CREATE TABLESPACE
postgres=# ALTER DATABASE catalogs SET TABLESPACE onNAS;
ALTER DATABASE
You see that I used the ALTER from David in last message, instead your suggestion of creating the whole database again.
Anyway, it seems the data from catalogs database is in the NAS.
See the following:
ofors@ev1:~$ sudo ls -l /home/ofors/Documents/nas/pgsql-data/
drwx------ 3 postgres postgres 4096 Apr 2 18:02 PG_9.2_201204301
ofors@ev1:~$ sudo du -sh /home/ofors/Documents/nas/pgsql-data/PG_9.2_201204301
467M /home/ofors/Documents/nas/pgsql-data/PG_9.2_201204301
postgres@ev1:~/9.2/main$ cd /var/lib/postgresql/9.2/main
postgres@ev1:~/9.2/main$ ls -ltr
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_snapshots
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_serial
-rw------- 1 postgres postgres 4 Aug 27 2014 PG_VERSION
drwx------ 2 postgres postgres 4096 Aug 27 2014 pg_twophase
drwx------ 4 postgres postgres 4096 Aug 27 2014 pg_multixact
drwx------ 2 postgres postgres 4096 Sep 3 2014 pg_clog
drwx------ 2 postgres postgres 4096 Sep 3 2014 pg_subtrans
drwx------ 3 postgres postgres 4096 Mar 27 13:57 pg_xlog
drwx------ 2 postgres postgres 4096 Apr 2 17:56 pg_tblspc
drwx------ 6 postgres postgres 4096 Apr 2 18:01 base
-rw------- 1 postgres postgres 91 Apr 2 18:19 postmaster.pid
drwx------ 2 postgres postgres 4096 Apr 2 18:19 pg_notify
-rw------- 1 postgres postgres 133 Apr 2 18:19 postmaster.opts
drwx------ 2 postgres postgres 4096 Apr 2 18:19 global
drwx------ 2 postgres postgres 4096 Apr 2 19:17 pg_stat_tmp
postgres@ev1:~/9.2/main$ du -sh ./*
19M ./base
448K ./global
624K ./pg_clog
28K ./pg_multixact
12K ./pg_notify
4.0K ./pg_serial
4.0K ./pg_snapshots
36K ./pg_stat_tmp
176K ./pg_subtrans
4.0K ./pg_tblspc
4.0K ./pg_twophase
4.0K ./PG_VERSION
129M ./pg_xlog
4.0K ./postmaster.opts
4.0K ./postmaster.pid
./base has pased from 485M to 19M, and PG_9.2_201204301 is now 467M, which seems to be consistent.
Also, I have double-checked with pgadmin3, and the database catalogs is now assigned to the tablespace onnas, while the other database I have (postgres) is still with pg_default.
Two only questions remain for me:
1) could you confirm that I don't have to mount --bind /var/lib/postgresql/9.2/main ?
2) on my my /etc/fstab here is the current line for my NAS:
nas_ip:/volume1/data /home/ofors/Documents/nas nfs
Which NFS client and server (on NAS side) options/arguments do you suggest for optimizing performance? Or in other words, for minimizing database corruption in case of NAS (note that NAS drives are in RAID6) or computer failure?
Thanks so much in advance,
--
Octavi Fors
--
Octavi Fors
On Thu, Apr 2, 2015 at 4:54 PM, John McKown <john.archie.mckown@gmail.com> wrote:
On Thu, Apr 2, 2015 at 3:01 PM, Octavi Fors <octavi@live.unc.edu> wrote:
> Hi,
>
> this is somehow overlapping one thread which was already posted in this list
>here.
>
> However, I'm newbie in PostgreSQL and would need some help from experts on
> two aspects. I apologize if these were already implicitely mentioned in the
> thread above.
>
> My situation is the following:
> 1-running postgresql-9.2 server under my Ubuntu 12.04 LTS desktop,
I'm running release 9.4 on Fedora 21, but hopefully what I can test
will be of some use to you.
> 2-user postgres created on the system,
Good.
> 3-two databases with several tables created, populated and owned by
> postgres,
> 4-these databases can be queried (SELECT, INSERT, etc.) by any system user
> of my desktop.
>
> Now here are my two questions:
>
> a) how can I know where my two databases are stored (I presume in a
> directory somewhere in my desktop path)?
You might want to read: https://help.ubuntu.com/community/PostgreSQL
They will be stored in the default location. On Fedora, this is
/var/lib/pgsql/data. I don't know what it is on Ubuntu, but you can
find out by using psql. Perhaps something like:
sudo su - postgres -c 'SHOW data_directory;'
Just using my normal id on Fedora, which is a PostgreSQL (not UNIX)
super user, I can see:
tsh009=# SHOW data_directory;
data_directory
---------------------
/var/lib/pgsql/data
(1 row)
tsh009=#
>
> b) this is the though one (at least for me ;) For data size reasons, I want
> to store my two databases in a NAS which I have mounted via NFS, but still
> keeping the postgresql server on my desktop.
Well, if you insist. But I would not move the default data there. I'd
keep it local. See below for an alternative.
> I've seen in this message of the thread above, that NFS noac mounting option
> is highly recommended.
> Apart from this, I don't see how to migrate the databases from my desktop
> directory determined in a) to my NAS. Could someone please provide the steps
> to accomplish that?
Well, there are a couple of approaches. Both will require UNIX root to
accomplish. If you are running SELinux enabled & enforcing, it is even
more complicated. But basically create an new, empty subdirectory on
your NAS box. Look at the owner & group on the directory shown above
(/var/lib/pgsql/data) and make it the new directory have the same
information. Something like:
sudo mkdir -p /NAS-box/pgsql-data
sudo chown --reference /var/lib/pgsql/data /NAS-box/pgsql-data
This sets up the new NAS-box/pgsql-data directory and assigns it the
proper owner:group for use by the server.
=== Moving the data - BAD IDEA, IMO ==
#stop the postgresql server on your system, however you do that. I
don't know Ubuntu.
sudo cp -a /var/lib/pgsql/data/* /NAS-box/pgsql-data
sudo cp -a /var/lib/pgsql/data/.* /NAS-box/pgsql-data
sudo mount --bind /var/lib/pgsql/data /NAS-box/pgsql-data
sudo restorecon -R /var/lib/pgsql/data # restore SELinux attributes
Commands #1 and #2 copy all the data to the new directory.
Command #3 does a "bind" mount so that any reference to
/var/lib/pgsql/data is redirected to /NAS-box/pgsql
Command #4 is if you run with SELinux.
Update your fstab to maintain the bind mount when you reboot. The
entry will look something like:
/NAS-box/pgsql-data /var/lib/pgsql/data none bind
=== THE ABOVE IS A BAD IDEA ===
=== Decent idea: ===
Create the NAS directory as above. Do _NOT_ copy anything into it! In
psql, as a postgres super user, create a new TABLESPACE
ref: http://www.postgresql.org/docs/9.2/interactive/sql-createtablespace.html
CREATE TABLESPACE onNAS LOCATION '/NAS-box/pgsql-data';
CREATE DATABASE somedb TABLESPACE onNAS;
\c somedb --connect to new database stored on the NAS
CREATE TABLE sometable ... ;
Now all the stuff in the "somedb" data base will reside on your NAS
box. Now all you need worry about is that it is reliable and fast
enough. Hopefully on at least a 1Gb ethernet.
In this case, I don't know the SELinux commands to set the SELinux
attributes. It is complicated.
=== Opinion.
I have a NAS box. But I would worry about responsiveness. What is
better, IMO, is an external SATA connected DAS box. DAS is "Direct
Attached Storage". Many PCs have a eSATA port on the back side. You
connect your DAS box to that will an eSATA cable. Now you have an
external disk expansion which runs at full SATA speed, just like an
internal disk drive. It's just an alternative. But you'd do the same
thing as with the NAS to get data onto it. Well, except that you could
dedicate an entire filesystem on the DAS to the /var/lib/pgsql/data
with something like:
# /dev/sd?n is the value for the DAS box.
sudo mkfs.ext4 /dev/sd?n #create new filesystem on DAS
sudo mount /dev/sd?n /tmp #mount it
sudo cp -a /var/lib/pgsql/data/* /tmp
sudo cp -a /var/lib/pgsql/data/.* /tmp
sudo umount /tmp
sudo mount /dev/sd?n /var/lib/pgsql/data #mount it
sudo restorecon -R /var/lib/pgsql/data # update SELinux attributes
The restorecon is only needed if you run SELinux--
>
>
> Thanks so much in advance,
>
> --
> Octavi Fors
>
If you sent twitter messages while exploring, are you on a textpedition?
He's about as useful as a wax frying pan.
10 to the 12th power microphones = 1 Megaphone
Maranatha! <><
John McKown
On Thu, Apr 2, 2015 at 7:09 PM, Octavi Fors <octavi@live.unc.edu> wrote: > Thanks John for your extensive and helpful response. > <snip> > You see that I used the ALTER from David in last message, instead your > suggestion of creating the whole database again. Looks good! <snip> > > Two only questions remain for me: > > 1) could you confirm that I don't have to mount --bind > /var/lib/postgresql/9.2/main ? If it is working for you now, then you don't need to mess with the fstab or the mount --bind at all. > > 2) on my my /etc/fstab here is the current line for my NAS: > nas_ip:/volume1/data /home/ofors/Documents/nas nfs > > Which NFS client and server (on NAS side) options/arguments do you suggest > for optimizing performance? Or in other words, for minimizing database > corruption in case of NAS (note that NAS drives are in RAID6) or computer > failure? Hum, performance is a bit over my head on disk drives, especially NAS. I have a small NAS, but my main 2Tb disk is eSATA. My fstab entry for the NAS just looks like: smartstor1:/VOLUME1/DV7T /SmartStor1/Volume1/DV7T nfs user,rw,noauto,noexec,nosuid 0 0 which is basically what you have, performance wise, as best as I can tell. Oh, are you going to try to share a single data base file with different PostgreSQL servers on different machines __AT THE SAME TIME__??? I think you're going to "Corruption City". There are locks which work fairly well on local disks (to share something like a file or directory) which don't work very well on some NAS boxes. At least, that is what Dr. Richard Hipp, who wrote and maintains SQLite, maintains in his support forum. And he is much brighter than I! > > > Thanks so much in advance, > > -- > Octavi Fors > > On Thu, Apr 2, 2015 at 4:54 PM, John McKown <john.archie.mckown@gmail.com> > wrote: >> >> On Thu, Apr 2, 2015 at 3:01 PM, Octavi Fors <octavi@live.unc.edu> wrote: >> > Hi, >> > >> > this is somehow overlapping one thread which was already posted in this >> > list >> >here. >> > >> > However, I'm newbie in PostgreSQL and would need some help from experts >> > on >> > two aspects. I apologize if these were already implicitely mentioned in >> > the >> > thread above. >> > >> > My situation is the following: >> > 1-running postgresql-9.2 server under my Ubuntu 12.04 LTS desktop, >> >> I'm running release 9.4 on Fedora 21, but hopefully what I can test >> will be of some use to you. >> >> > 2-user postgres created on the system, >> >> Good. >> >> > 3-two databases with several tables created, populated and owned by >> > postgres, >> > 4-these databases can be queried (SELECT, INSERT, etc.) by any system >> > user >> > of my desktop. >> > >> > Now here are my two questions: >> > >> > a) how can I know where my two databases are stored (I presume in a >> > directory somewhere in my desktop path)? >> >> You might want to read: https://help.ubuntu.com/community/PostgreSQL >> >> They will be stored in the default location. On Fedora, this is >> /var/lib/pgsql/data. I don't know what it is on Ubuntu, but you can >> find out by using psql. Perhaps something like: >> >> sudo su - postgres -c 'SHOW data_directory;' >> >> Just using my normal id on Fedora, which is a PostgreSQL (not UNIX) >> super user, I can see: >> >> tsh009=# SHOW data_directory; >> data_directory >> --------------------- >> /var/lib/pgsql/data >> (1 row) >> >> tsh009=# >> >> >> > >> > b) this is the though one (at least for me ;) For data size reasons, I >> > want >> > to store my two databases in a NAS which I have mounted via NFS, but >> > still >> > keeping the postgresql server on my desktop. >> >> Well, if you insist. But I would not move the default data there. I'd >> keep it local. See below for an alternative. >> >> > I've seen in this message of the thread above, that NFS noac mounting >> > option >> > is highly recommended. >> > Apart from this, I don't see how to migrate the databases from my >> > desktop >> > directory determined in a) to my NAS. Could someone please provide the >> > steps >> > to accomplish that? >> >> Well, there are a couple of approaches. Both will require UNIX root to >> accomplish. If you are running SELinux enabled & enforcing, it is even >> more complicated. But basically create an new, empty subdirectory on >> your NAS box. Look at the owner & group on the directory shown above >> (/var/lib/pgsql/data) and make it the new directory have the same >> information. Something like: >> >> sudo mkdir -p /NAS-box/pgsql-data >> sudo chown --reference /var/lib/pgsql/data /NAS-box/pgsql-data >> >> This sets up the new NAS-box/pgsql-data directory and assigns it the >> proper owner:group for use by the server. >> >> === Moving the data - BAD IDEA, IMO == >> >> #stop the postgresql server on your system, however you do that. I >> don't know Ubuntu. >> >> sudo cp -a /var/lib/pgsql/data/* /NAS-box/pgsql-data >> sudo cp -a /var/lib/pgsql/data/.* /NAS-box/pgsql-data >> sudo mount --bind /var/lib/pgsql/data /NAS-box/pgsql-data >> sudo restorecon -R /var/lib/pgsql/data # restore SELinux attributes >> >> Commands #1 and #2 copy all the data to the new directory. >> Command #3 does a "bind" mount so that any reference to >> /var/lib/pgsql/data is redirected to /NAS-box/pgsql >> Command #4 is if you run with SELinux. >> >> Update your fstab to maintain the bind mount when you reboot. The >> entry will look something like: >> >> /NAS-box/pgsql-data /var/lib/pgsql/data none bind >> >> === THE ABOVE IS A BAD IDEA === >> >> === Decent idea: === >> Create the NAS directory as above. Do _NOT_ copy anything into it! In >> psql, as a postgres super user, create a new TABLESPACE >> ref: >> http://www.postgresql.org/docs/9.2/interactive/sql-createtablespace.html >> >> CREATE TABLESPACE onNAS LOCATION '/NAS-box/pgsql-data'; >> CREATE DATABASE somedb TABLESPACE onNAS; >> \c somedb --connect to new database stored on the NAS >> CREATE TABLE sometable ... ; >> >> >> Now all the stuff in the "somedb" data base will reside on your NAS >> box. Now all you need worry about is that it is reliable and fast >> enough. Hopefully on at least a 1Gb ethernet. >> In this case, I don't know the SELinux commands to set the SELinux >> attributes. It is complicated. >> >> === Opinion. >> >> I have a NAS box. But I would worry about responsiveness. What is >> better, IMO, is an external SATA connected DAS box. DAS is "Direct >> Attached Storage". Many PCs have a eSATA port on the back side. You >> connect your DAS box to that will an eSATA cable. Now you have an >> external disk expansion which runs at full SATA speed, just like an >> internal disk drive. It's just an alternative. But you'd do the same >> thing as with the NAS to get data onto it. Well, except that you could >> dedicate an entire filesystem on the DAS to the /var/lib/pgsql/data >> with something like: >> >> # /dev/sd?n is the value for the DAS box. >> sudo mkfs.ext4 /dev/sd?n #create new filesystem on DAS >> sudo mount /dev/sd?n /tmp #mount it >> sudo cp -a /var/lib/pgsql/data/* /tmp >> sudo cp -a /var/lib/pgsql/data/.* /tmp >> sudo umount /tmp >> sudo mount /dev/sd?n /var/lib/pgsql/data #mount it >> sudo restorecon -R /var/lib/pgsql/data # update SELinux attributes >> >> The restorecon is only needed if you run SELinux >> >> >> > >> > >> > Thanks so much in advance, >> > >> > -- >> > Octavi Fors >> > >> >> >> >> -- >> If you sent twitter messages while exploring, are you on a textpedition? >> >> He's about as useful as a wax frying pan. >> >> 10 to the 12th power microphones = 1 Megaphone >> >> Maranatha! <>< >> John McKown > > > > > -- If you sent twitter messages while exploring, are you on a textpedition? He's about as useful as a wax frying pan. 10 to the 12th power microphones = 1 Megaphone Maranatha! <>< John McKown
On Apr 2, 2015, at 5:09 PM, Octavi Fors <octavi@live.unc.edu> wrote: > > And second, because I need the database to be accessible from two computers in the same LAN. If you do this, you will destroy your database[1]. Why not have the database running on one machine, all the time, potentially with a real disk subsystem then just access itfrom wherever on the LAN you need to? Postgresql is a client-server database, and you can access it over the network aseasily as you can from the machine it's running on. Cheers, Steve [1] Almost certainly, unless you make absolutely sure postgresql is only started on one machine at a time, amongst otherthings.
Thanks John for your extensive and helpful response.I have a NAS box. But I would worry about responsiveness. What is
better, IMO, is an external SATA connected DAS box. DAS is "Direct
Attached Storage". Many PCs have a eSATA port on the back side.as far as I understand eSATA is not an option for me. First because I already have bought the DS2415+ NAS, which does not has eSATA I/O :(
And second, because I need the database to be accessible from two computers in the same LAN.
This is new - and while the desire for using your multi-terrabyte device may make the risk of running over NFS potentially worthwhile there is no reasonable way to have two running databases share data files. You can share the NAS device and have each PostgreSQL instance consume an unshared portion of its resources.
You appear to either be "mis-speaking" or omitting potentially critically important details here...
1) could you confirm that I don't have to mount --bind /var/lib/postgresql/9.2/main ?
/var/lib/... is not on the NAS but, likely, on whatever your primary internal hard drive is. Note, the most important aspect of that fact is that your WAL gets written to your data directory and not to the tablespace on which the database tables reside. (i.e. WAL does not make it to NAS - unless you setup wal shipping).
2) on my my /etc/fstab here is the current line for my NAS:
nas_ip:/volume1/data /home/ofors/Documents/nas nfsWhich NFS client and server (on NAS side) options/arguments do you suggest for optimizing performance? Or in other words, for minimizing database corruption in case of NAS (note that NAS drives are in RAID6) or computer failure?
I am a little out of my league here but the main risk is that incomplete data is sent/received by/from the NAS. Once the data is in the NAS it is really no different than any other storage medium in terms of durability concerns. I do not really know how checkpoints and transient failed reads interact with PostgreSQL and what circumstances would prevent properly recorded WAL from being used to restore should a read/write failure occur.
David J.
Hi David, John et al.,
as far as I understand eSATA is not an option for me. First because I already have bought the DS2415+ NAS, which does not has eSATA I/O :(
And second, because I need the database to be accessible from two computers in the same LAN.
This is new - and while the desire for using your multi-terrabyte device may make the risk of running over NFS potentially worthwhile there is no reasonable way to have two running databases share data files. You can share the NAS device and have each PostgreSQL instance consume an unshared portion of its resources.You appear to either be "mis-speaking" or omitting potentially critically important details here...
My situation is the following:
-Two computers (C1 & C2) and NAS (with no eSATA I/O) on the same LAN.
-C1 acquires images from a telescope and periodically stores them via NFS in the NAS (no database involved here, just in the ext4 filesystem).
-C2 is a 12 xeon core-class server designed to analyze the stored images in the NAS, and compute astrometry & photometry measurements (catalogs & light curves) for every star & image. These measurements are inserted in the catalogs database inside the NAS.
-C2 is a 12 xeon core-class server designed to analyze the stored images in the NAS, and compute astrometry & photometry measurements (catalogs & light curves) for every star & image. These measurements are inserted in the catalogs database inside the NAS.
Therefore there's only *one* computer (C2) which will run postgresql server with the tablespace onNAS.
So does this approach sound like feasible if the NFS parameters are set properly?
I have a small NAS, but my main 2Tb disk is eSATA. My fstab entry for
the NAS just looks like:
smartstor1:/VOLUME1/DV7T /SmartStor1/Volume1/DV7T nfs
user,rw,noauto,noexec,nosuid 0 0
which is basically what you have, performance wise, as best as I can tell.
I see this message in this list any ideas suggesting to use the NFS parameters 'sync' (for synchronizing changes to a file) and 'noac' (for no caching).
Could you confirm that
nas_ip:/volume1/data /home/ofors/Documents/nas nfs noac,sync
would be good options for /etc/fstab?
Any additional NFS parameter?
Note, the most important aspect of that fact is that your WAL gets written to your data directory and not to the tablespace on which the database tables reside. (i.e. WAL does not make it to NAS - unless you setup wal shipping).
first time I hear about the importance of WAL and NFS.
I googled some and found this discussion about the topic.
Any ideas on how to include the options they mention (archinve_mode?) into NAS or /etc/fstab?
Thanks a lot in advance,
Octavi Fors
On Thu, Apr 2, 2015 at 8:47 PM, David G. Johnston <david.g.johnston@gmail.com> wrote:
Thanks John for your extensive and helpful response.I have a NAS box. But I would worry about responsiveness. What is
better, IMO, is an external SATA connected DAS box. DAS is "Direct
Attached Storage". Many PCs have a eSATA port on the back side.as far as I understand eSATA is not an option for me. First because I already have bought the DS2415+ NAS, which does not has eSATA I/O :(
And second, because I need the database to be accessible from two computers in the same LAN.This is new - and while the desire for using your multi-terrabyte device may make the risk of running over NFS potentially worthwhile there is no reasonable way to have two running databases share data files. You can share the NAS device and have each PostgreSQL instance consume an unshared portion of its resources.You appear to either be "mis-speaking" or omitting potentially critically important details here...1) could you confirm that I don't have to mount --bind /var/lib/postgresql/9.2/main ?/var/lib/... is not on the NAS but, likely, on whatever your primary internal hard drive is. Note, the most important aspect of that fact is that your WAL gets written to your data directory and not to the tablespace on which the database tables reside. (i.e. WAL does not make it to NAS - unless you setup wal shipping).2) on my my /etc/fstab here is the current line for my NAS:
nas_ip:/volume1/data /home/ofors/Documents/nas nfsWhich NFS client and server (on NAS side) options/arguments do you suggest for optimizing performance? Or in other words, for minimizing database corruption in case of NAS (note that NAS drives are in RAID6) or computer failure?I am a little out of my league here but the main risk is that incomplete data is sent/received by/from the NAS. Once the data is in the NAS it is really no different than any other storage medium in terms of durability concerns. I do not really know how checkpoints and transient failed reads interact with PostgreSQL and what circumstances would prevent properly recorded WAL from being used to restore should a read/write failure occur.David J.
On Fri, Apr 3, 2015 at 1:40 AM, Octavi Fors <octavi@live.unc.edu> wrote: > Hi David, John et al., <snip> > Oops, sorry yes I think I may "miss-spoke" when explaining my second reason > why not choosing eSATA. > My situation is the following: > > -Two computers (C1 & C2) and NAS (with no eSATA I/O) on the same LAN. > -C1 acquires images from a telescope and periodically stores them via NFS in > the NAS (no database involved here, just in the ext4 filesystem). > -C2 is a 12 xeon core-class server designed to analyze the stored images in > the NAS, and compute astrometry & photometry measurements (catalogs & light > curves) for every star & image. These measurements are inserted in the > catalogs database inside the NAS. > > Therefore there's only *one* computer (C2) which will run postgresql server > with the tablespace onNAS. > > So does this approach sound like feasible if the NFS parameters are set > properly? OK, it is very understandable why the images are on the NAS. It is the easiest way to share them. I guess you want the DB on the NAS simply because you don't have sufficient disk space on the disks connected to C2. > <snip> > Could you confirm that > nas_ip:/volume1/data /home/ofors/Documents/nas nfs noac,sync > would be good options for /etc/fstab? > > Any additional NFS parameter? Have you done a web search on "NFS Performance"? I got some good hits with Google. http://www.tldp.org/HOWTO/NFS-HOWTO/performance.html (a bit old, I've been told) http://www.cyberciti.biz/faq/linux-unix-tuning-nfs-server-client-performance/ Mentions "noatime" and "nodiratime" to not update the last access date/time on files & directories, saving bandwidth. A good explanation of the NFS mount options, IMO, are on this site: http://www.dbaexpert.com/blog/nfs-options-for-performance/ Some interesting "speed test" code: https://github.com/sabujp/nfsSpeedTest > <snip> > Thanks a lot in advance, > -- > Octavi Fors -- If you sent twitter messages while exploring, are you on a textpedition? He's about as useful as a wax frying pan. 10 to the 12th power microphones = 1 Megaphone Maranatha! <>< John McKown