Re: SSD + RAID
От | Bruce Momjian |
---|---|
Тема | Re: SSD + RAID |
Дата | |
Msg-id | 201003020333.o223Xrf20941@momjian.us обсуждение исходный текст |
Ответ на | Re: SSD + RAID (Ron Mayer <rm_pg@cheapcomplexdevices.com>) |
Ответы |
Re: SSD + RAID
Re: SSD + RAID |
Список | pgsql-performance |
Ron Mayer wrote: > Bruce Momjian wrote: > > Greg Smith wrote: > >> Bruce Momjian wrote: > >>> I have added documentation about the ATAPI drive flush command, and the > >> > >> If one of us goes back into that section one day to edit again it might > >> be worth mentioning that FLUSH CACHE EXT is the actual ATAPI-6 command > >> that a drive needs to support properly. I wouldn't bother with another > >> doc edit commit just for that specific part though, pretty obscure. > > > > That setting name was not easy to find so I added it to the > > documentation. > > If we're spelling out specific IDE commands, it might be worth > noting that the corresponding SCSI command is "SYNCHRONIZE CACHE"[1]. > > > Linux apparently sends FLUSH_CACHE commands to IDE drives in the > exact sample places it sends SYNCHRONIZE CACHE commands to SCSI > drives[2]. > > It seems that the same file systems, SW raid layers, > virtualization platforms, and kernels that have a problem > sending FLUSH CACHE commands to SATA drives have he same exact > same problems sending SYNCHRONIZE CACHE commands to SCSI drives. > With the exact same effect of not getting writes all the way > through disk caches. I always assumed SCSI disks had a write-through cache and therefore didn't need a drive cache flush comment. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com PG East: http://www.enterprisedb.com/community/nav-pg-east-2010.do
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