On 24 Apr 2009 at 16:06, Konrad Rzeszutek wrote: > > On Fri, Apr 24, 2009 at 02:14:43PM -0400, Donald Williams wrote: > > Have you tried increasing the disk readahead value? > > #blockdev --setra X /dev/<multipath device> > > > > The default is 256. Use --getra to see current setting. > > > > Setting it too high will probably hurt your database performance. Since > > databases tend to be random, not sequential. > > I would think that the databases would open the disks with O_DIRECT > bypassing the block cache (And hence the disk readahead value isn't used > at all).
Hi, first a silly question: Shouldn't the read-ahead on the server be as least as hight as the setting on the client to provide any benefit? And two interesting numbers: On one of our busy databases the the read:write ratio is about 10:1 and the tables are severely fragmented On our Linux servers using iSCSI the read:write ratio is about 1:10 because the machines have several GIGs of RAM and the disk caching is very efficient. So the machine just has to send out the writes... Regards, Ulrich --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to open-iscsi@googlegroups.com To unsubscribe from this group, send email to open-iscsi+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/open-iscsi -~----------~----~----~----~------~----~------~--~---
