What happens if you use a hardware raid, should the stride option be considered? It seems you are referring to software raid, correct? TIA <div class="gmail_quote">On Thu, Jun 19, 2008 at 7:42 AM, Theodore Tso <<a href="mailto:tytso@mit.edu">tytso@mit.edu</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="Ih2E3d">On Thu, Jun 19, 2008 at 06:21:24AM -0400, Mag Gam wrote: > ok, in a way its like a stripe? I though when you do a stripe you put the > metadata on number of disks too. How is that different? Is there a diagram I > can refer to? </div>Yes, which is why the mke2fs man page states: stride=<stripe-size> Configure the filesystem for a RAID array with <stripe-size> filesystem blocks per stripe. So if the size of a stripe on each a disk is 64k, and you are using a 4k filesystem blocksize, then 64k/4k == 16, and that would be an "ideal" stride size, in that for each successive block group, the inode and block bitmap would increased by an offset of 16 blocks from the beginning of the block group. The reason for doing this is to avoid problems where the block bitmap ends up on the same disk for every single block group. The classic case where this would happen is if you have a 5 disks in a RAID 5 configuration, which means with 4 disks per stripe, and 8192 blocks in a blockgroup, then if the block bitmap is always at the same offset from the beginning of the block group, one disk will get all of the block bitmaps, and that ends up being a major hot spot problem for the hard drive. As it turns out, if you use 4 disks in a RAID 5 configuration, or 6 disks in a RAID 5 configuration, this problem doesn't arise at all, and you don't need to use the stride option. And in most cases, simply using a stride=1, that is actually enough to make sure that each block and inode bitmaps will get forced onto successively different disks. With ext4's flex_bg enhancement, the need to specify stride option of RAID arrays will also go away. - Ted </blockquote></div>