On Thu, Feb 24, 2011 at 07:23:54PM +0100, Christer Solskogen wrote: > On Thu, Feb 24, 2011 at 8:55 AM, Jeremy Chadwick > <free...@jdc.parodius.com> wrote: > > > > > # Set TXG write limit to a lower threshold. This helps "level out" > > # the throughput rate (see "zpool iostat"). A value of 256MB works well > > # for systems with 4GB of RAM, while 1GB works well for us w/ 8GB on > > # disks which have 64MB cache. > > vfs.zfs.txg.write_limit_override=1073741824 > > > > > > Sorry if you have said this before, but could you elaborate a bit > about this number? For instance, how much does the cache on the disk > has to say. > In my case: 3x1.5TB raidz with WD15EADS-00R6B0 which has 32MB cache > and 12GB memory. What would you recommend and why.
There's no real way to provide an in-depth analysis of this number; that is to say, hard disk parameters (RPM, cache, and overall performance of the drive (highly dependent upon on-disk firmware)) ultimately dictates what's "best" for this number. I also imagine number of disks plays a role as well This is why I advocate not messing with it unless you want to try and "level out" throughput. The value itself is literally 1024*1024*1024 (1GB). Don't think this is some magic number; it's just what I came up with. You can search the FreeBSD lists for references to the variable itself and find other people advocating values like ~33MByte, etc.. All depends on how you want the system to behave. I don't particularly like watching the system behave like I described (you snipped that portion of my text), which is why I use this variable. -- | Jeremy Chadwick j...@parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP 4BD6C0CB | _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
