Re: HDD vs SSD without explanation

2018-01-15 17:58 GMT-08:00 Justin Pryzby <pryzby@telsasoft.com>:
> On Mon, Jan 15, 2018 at 05:19:59PM -0800, Neto pr wrote:
>> >> Can you reproduce the speed difference using dd ?
>> >> time sudo dd if=/dev/sdX of=/dev/null bs=1M count=32K
>> >> skip=$((128*$RANDOM/32)) # set bs to optimal_io_size
>> >
>> > Still I would have expected somewhat similar results in the outcome, so yes,
>> > it is weird that the SAS drive doubles the SSD performance. That is why I
>> > think there must be something else going on during your tests on the SSD
>> > server. It can also be that the SSD isn't working properly or you are
>> > running an suboptimal OS+server+controller configuration for the drive.
>>
>> Ok.
>>
>> Can you help me to analyze the output of the command: dd if=/dev/sdX
>> of=/dev/null bs=1M count=32K skip=$((128*$RANDOM/32)) # set bs to
>> optimal_io_size
>
> You should run the "dd" without the DB or anything else using the drive.  That
> gets peformance of the drive, without the DB.

Oh important observation,..

>
> You should probably rerun the "dd" command using /dev/sdb1 if there's an
> partition table on top (??).
>
> I'm still wondering about these:

See Below:
------------========= SSD SATA 500GB 6 Gb/s
=======------------------------------
root@hp2ml110deb:/etc# time sudo dd if=/dev/sdb of=/dev/null bs=1M
count=32K skip=$((128*$RANDOM/32)) # set bs to optimal_io_size
32768+0 records in
32768+0 records out
34359738368 bytes (34 GB) copied, 71.0047 s, 484 MB/s

real    1m11.109s
user    0m0.008s
sys     0m16.584s
root@hp2ml110deb:/etc# time sudo dd if=/dev/sdb of=/dev/null bs=1M
count=32K skip=$((128*$RANDOM/32)) # set bs to optimal_io_size
32768+0 records in
32768+0 records out
34359738368 bytes (34 GB) copied, 70.937 s, 484 MB/s

real    1m11.089s
user    0m0.012s
sys     0m16.312s
root@hp2ml110deb:/etc#


------------========= HDD SAS 300GB 12 Gb/s
=======------------------------------
root@deb:/home/user1#  time sudo dd if=/dev/sda2 of=/dev/null bs=1M
count=32K skip=$((128*$RANDOM/32)) # set bs to optimal_io_size

32768+0 records in
32768+0 records out
34359738368 bytes (34 GB) copied, 147.232 s, 233 MB/s

real    2m27.277s
user    0m0.036s
sys     0m23.096s
root@deb:/home/user1#
root@deb:/home/user1#  time sudo dd if=/dev/sda2 of=/dev/null bs=1M
count=32K skip=$((128*$RANDOM/32)) # set bs to optimal_io_size
32768+0 records in
32768+0 records out
34359738368 bytes (34 GB) copied, 153.698 s, 224 MB/s

real    2m33.766s
user    0m0.032s
sys     0m22.812s
root@deb:/home/user1#
---------------------------------------------  END
---------------------------------------------------

I had not spoken, but my SAS HDD is connected to the HBA Controler,
through a SATA adapter, because the cable kit I would have to use and
it would be correct, was no available at the supplier,  so it sent the
SAS HDD with a SATA adapter. I found it strange that the speed of SAS
was below the SSD, and even then it can execute the query much faster.



>
> On Sun, Jan 14, 2018 at 09:09:41PM -0600, Justin Pryzby wrote:
>> What about sdb partitions/FS?
>
>> > > readahead?  blockdev --getra
>>
>> > > If you're running under linux, maybe you can just send the output of:
>> > > for a in /sys/block/sdX/queue/*; do echo "$a `cat $a`"; done
>> > > or: tail
/sys/block/sdX/queue/{minimum_io_size,optimal_io_size,read_ahead_kb,scheduler,rotational,max_sectors_kb,logical_block_size,physical_block_size}
>
> Justin