2) If we have a filesystem + logical volume manager over raid device, this could make less CPU/IO use if we don´t have a filesystem, this could make less CPU/IO use the question is, this really make more performace? we don´t know, must benchmark with each filesystem, logical volume, device.... this is a good 'feature', but i don´t think we will get more performace... (any benchmark to confirm it?) 2011/1/18 NeilBrown <neilb@xxxxxxx>: > 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 > -- 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
