> -----Original Message----- > From: centos-bounces at centos.org > [mailto:centos-bounces at centos.org] On Behalf Of Aleksandar Milivojevic > Sent: Monday, January 08, 2007 1:00 PM > To: centos at centos.org > Subject: RE: [CentOS] Disk Elevator > > Quoting "Ross S. W. Walker" <rwalker at medallion.com>: > > > The biggest performance gain you can achieve on a raid > array is to make > > sure you format the volume aligned to your raid stripe > size. For example > > if you have a 4 drive raid 5 and it is using 64K chunks, your stripe > > size will be 256K. Given a 4K filesystem block size you > would then have > > a stride of 64 (256/4), so when you format your volume: > > > > Mke2fs -E stride=64 (other needed options -j for ext3, -N > <# of inodes> > > for extended # of i-nodes, -O dir_index speeds up directory > searches for > > large # of files) /dev/XXXX > > Shouldn't the argument for stride option be how many file system > blocks there is per stripe? After all, there's no way for OS > to guess > what RAID level you are using. For 4 disk RAID5 with 64k chunks and > 4k file system blocks you have only 48 file system blocks per stripe > ((4-1)x64k/4k=48). So it should be -E stride=48 in this particular > case. If it was 4 disk RAID0 array, than it would be 64 > (4x64k/4k=64). If it was 4 disk RAID10 array, than it would be 32 > ((4/2)*64k/4k=32). Or at least that's the way I understood it by > reading the man page. You are correct, leave one of the chunks off for the parity, so for 4 disk raid5 stride=48. I had just computed all 4 chunks as part of the stride. BTW that parity chunk still needs to be in memory to avoid the read on it, no? In that case wouldn't a stride of 64 help in that case? And if the stride leaves out the parity chunk then will not successive read-aheads cause a continuous wrap of the stripe which will negate the effect of the stride by not having the complete stripe cached? -Ross ______________________________________________________________________ This e-mail, and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail, you are hereby notified that any dissemination, distribution or copying of this e-mail, and any attachments thereto, is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender and permanently delete the original and any copy or printout thereof.