От: david@lang.hm
Тема: Re: Raid 10 chunksize
Дата: ,
Msg-id: alpine.DEB.1.10.0904011337310.28893@asgard.lang.hm
(см: обсуждение, исходный текст)
Ответ на: Re: Raid 10 chunksize  (Mark Kirkwood)
Ответы: 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, )

On Wed, 1 Apr 2009, Mark Kirkwood wrote:

> 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!

given how _horrible_ ext3 is with fsync, I can belive it more easily with
fsync turned on than with it off.

David Lang

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


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