On Tue, 18 Jan 2011 22:59:07 +0700 Igor Podlesny <for.poige+linux@xxxxxxxxx> wrote: > I had experience of using FreeBSD's vinum (another software RAID). > Its author, Greg Lehey, stated in vinum's manual: "... A good > guideline for stripe size is between 256 kB and 512 kB. Avoid powers > of 2, however: they tend to cause all superblocks to be placed on the > first subdisk. ..." > > Meanwhile, with LSR we're given exactly 2^n choices, for e. g., > neither 768 KiB, nor 387 KiB won't go: "mdadm: invalid chunk/rounding > value: 387". > > So, why... ($Subj) and how complex would it be to abolish this > restriction? I think this could be a key to performance increase. > > P. S. Thanks a ton for LSR, Neil, BTW. :-) > 1/ The rationale given by Greg for non-power-of-two chunk sizes is not so relevant for Linux I think. The more common filesystems can be told that the device is a RAID and can deliberately offset the extra super blocks so they don't all end up on the one device. 2/ Power-off-two is required simply because it was easier to code. The restriction was dropped for RAID0 a year or more ago. The restriction could be dropped for RAID4/5/6 and RAID10 relatively easily. It would just require a thorough code review and changing a few 'mask' and 'shift' operations to divisions. 3/ You are welcome. NeilBrown -- 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
