От: Mark Kirkwood
Тема: Re: Raid 10 chunksize
Дата: ,
Msg-id: 49D31E85.8050405@paradise.net.nz
(см: обсуждение, исходный текст)
Ответ на: Re: Raid 10 chunksize  (Scott Carey)
Ответы: Re: Raid 10 chunksize  (Stef Telford)
Re: Raid 10 chunksize  ()
Список: pgsql-performance

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Raid 10 chunksize  (Mark Kirkwood, )
 Re: Raid 10 chunksize  (Scott Carey, )
  Re: Raid 10 chunksize  (David Rees, )
   Re: Raid 10 chunksize  (Greg Smith, )
 Re: Raid 10 chunksize  (Scott Marlowe, )
  Re: Raid 10 chunksize  (Mark Kirkwood, )
   Re: Raid 10 chunksize  (Jerry Champlin, )
   Re: Raid 10 chunksize  (Mark Kirkwood, )
    Re: Raid 10 chunksize  (Scott Carey, )
     Re: Raid 10 chunksize  (Mark Kirkwood, )
      Re: Raid 10 chunksize  (Mark Kirkwood, )
 Re: Raid 10 chunksize  (Greg Smith, )
  Re: Raid 10 chunksize  (Scott Carey, )
   Re: Raid 10 chunksize  (Merlin Moncure, )
    Re: Raid 10 chunksize  (Scott Carey, )
     Re: Raid 10 chunksize  (Merlin Moncure, )
     Re: Raid 10 chunksize  (Scott Carey, )
  Re: Raid 10 chunksize  (Mark Kirkwood, )
   Re: Raid 10 chunksize  (Greg Smith, )
    Re: Raid 10 chunksize  (Mark Kirkwood, )
 Re: Raid 10 chunksize  (Stef Telford, )
  Re: Raid 10 chunksize  (Mark Kirkwood, )
   Re: Raid 10 chunksize  (Scott Carey, )
    Re: Raid 10 chunksize  (Scott Carey, )
     Re: Raid 10 chunksize  (Mark Kirkwood, )
      Re: Raid 10 chunksize  (Stef Telford, )
       Re: Raid 10 chunksize  (Greg Smith, )
        Re: Raid 10 chunksize  (Stef Telford, )
         Re: Raid 10 chunksize  (Scott Marlowe, )
          Re: Raid 10 chunksize  (Stef Telford, )
           Re: Raid 10 chunksize  (Scott Marlowe, )
            Re: Raid 10 chunksize  (Greg Smith, )
             Re: Raid 10 chunksize  (Matthew Wakeling, )
              Re: Raid 10 chunksize  (Scott Marlowe, )
            Re: Raid 10 chunksize  (Scott Carey, )
             Re: Raid 10 chunksize  (, )
             Re: Raid 10 chunksize  (Scott Marlowe, )
           Re: Raid 10 chunksize  (Matthew Wakeling, )
            Re: Raid 10 chunksize  (Scott Marlowe, )
            Re: Raid 10 chunksize  (Stef Telford, )
            Re: Raid 10 chunksize  (Scott Carey, )
          Re: Raid 10 chunksize  (Matthew Wakeling, )
         Re: Raid 10 chunksize  (Scott Carey, )
          Re: Raid 10 chunksize  (Greg Smith, )
           Re: Raid 10 chunksize  (James Mansion, )
            Re: Raid 10 chunksize  (Greg Smith, )
           Re: Raid 10 chunksize  (Scott Carey, )
            Re: Raid 10 chunksize  (Greg Smith, )
           Re: Raid 10 chunksize  (Ron Mayer, )
            Re: Raid 10 chunksize  (Hannes Dorbath, )
       Re: Raid 10 chunksize  (Stef Telford, )
        Re: Raid 10 chunksize  (Stef Telford, )
         Re: Raid 10 chunksize  (Scott Carey, )
       Re: Raid 10 chunksize  (Mark Kirkwood, )
      Re: Raid 10 chunksize  (, )
       Re: Raid 10 chunksize  (, )
 Re: Raid 10 chunksize  (Greg Smith, )
  Re: Raid 10 chunksize  (, )
   Re: Raid 10 chunksize  (Greg Smith, )
   Re: Raid 10 chunksize  (Scott Carey, )

Scott Carey wrote:
>
> A little extra info here >>  md, LVM, and some other tools do not allow the
> file system to use write barriers properly.... So those are on the bad list
> for data integrity with SAS or SATA write caches without battery back-up.
> However, this is NOT an issue on the postgres data partition.  Data fsync
> still works fine, its the file system journal that might have out-of-order
> writes.  For xlogs, write barriers are not important, only fsync() not
> lying.
>
> As an additional note, ext4 uses checksums per block in the journal, so it
> is resistant to out of order writes causing trouble.  The test compared to
> here was on ext4, and most likely the speed increase is partly due to that.
>
>

[Looks at  Stef's  config - 2x 7200 rpm SATA RAID 0]  I'm still highly
suspicious of such a system being capable of outperforming one with the
same number of (effective) - much faster - disks *plus* a dedicated WAL
disk pair... unless it is being a little loose about fsync! I'm happy to
believe ext4 is better than ext3 - but not that much!

However, its great to have so many different results to compare against!

Cheers

Mark



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