On 7 June 2012 06:53, Peter Grandi <pg@xxxxxxxxxxxxxxxxxxx> wrote: […] > «A good guideline for stripe size is between 256 kB and 512 > kB.» > > It is very important to note here that "stripe size" in Vinum > means "chunk size" in MD. For many workloads that is too large a > chunk size. It depends on number of files in working set. I still can't see reasons to have 4 KiB chunk (or stripe size) for newsdir or maildir with the hell a lot of tiny files, really — having enough of them anyways guarantees equal load distribution among all of the disks even with rather large chunk size. But with 4 KiB _every_ I/O-op would involve several disks, and again I don't consider it's "nice". > «Avoid powers of 2, however: they tend to cause all superblocks > to be placed on the first subdisk. …» — http://goo.gl/sTHxY > >> P. S. Alas, LSR doesn't support anything but powers of 2 for >> chunk sizes, but according to Neil Brown, it can be relatively >> easy changed. > > Some important Linux filesystems try to align metadata to chunk > boundaries instead, for example 'ext3' with 'stride=' and XFS > with 'su='. They try, for sure, but try is still a try. For e. g., you pvmove'd your LVM with XFS from one RAID to another one having different "layout", things can just stop working well all of the sudden. Another drawback of 2^n chunk sizes is extending gap between them: …1024…2048…4096…8192…. You just can't go and try something like 1731 or 3333 KiB for chunk size. -- -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
