maybe we could do betters read/write algorithm for devices (hard disks / solid state disks) for example (round robin, closer head, minimal read/write time) that make a more optimized operation with mixed disks array (ssd+hdd array) for raid 0,1,10,5,6,x+y 2011/1/18 John Robinson <john.robinson@xxxxxxxxxxxxxxxx>: > On 18/01/2011 15:59, Igor Podlesny 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. > > You're slightly confusing things. Stripe size and chunk size are different > things, but related. Stripe size = number of data discs * chunk size. Linux > software RAID does insist on a power of two chunk size, which is almost > certainly done for performance reasons, but obviously it can't insist on a > power of two stripe size, e.g. a 3-disc RAID-0, 4-disc RAID-5 or 5-disc > RAID-6 would all have 3 data discs so the stripe size won't be a power of > two. > > Secondly, as far as I know all Linux filesystems are RAID-aware so know how > to distribute their superblocks and other metadata evenly across all the > discs, so they've already got any performance improvement that might be had. > > Cheers, > > John. > > -- > 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 > -- Roberto Spadim Spadim Technology / SPAEmpresarial -- 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
