Re: file system and raid performance

Mark Mielke wrote:
> Greg Smith wrote:
> > On Fri, 15 Aug 2008, Bruce Momjian wrote:
> >> 'data=writeback' is the recommended mount method for that file
> >> system, though I see that is not mentioned in our official
> >> documentation.
> > While writeback has good performance characteristics, I don't know
> > that I'd go so far as to support making that an official
> > recommendation. The integrity guarantees of that journaling mode are
> > pretty weak. Sure the database itself should be fine; it's got the
> > WAL as a backup if the filesytem loses some recently written bits.
> > But I'd hate to see somebody switch to that mount option on this
> > project's recommendation only to find some other files got corrupted
> > on a power loss because of writeback's limited journalling. ext3 has
> > plenty of problem already without picking its least safe mode, and
> > recommending writeback would need a carefully written warning to that
> > effect.
>
> To contrast - not recommending it means that most people unaware will be
> running with a less effective mode, and they will base their performance
> measurements on this less effective mode.
>
> Perhaps the documentation should only state that "With ext3,
> data=writeback is the recommended mode for PostgreSQL. PostgreSQL
> performs its own journalling of data and does not require the additional
> guarantees provided by the more conservative ext3 modes. However, if the
> file system is used for any purpose other than PostregSQL database
> storage, the data integrity requirements of these other purposes must be
> considered on their own."
>
> Personally, I use data=writeback for most purposes, but use data=journal
> for /mail and /home. In these cases, I find even the default ext3 mode
> to be fewer guarantees than I am comfortable with. :-)

I have documented this in the WAL section of the manual, which seemed
like the most logical location.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +