Okay, not it is confusing.. having two different answers to this question :) Which answer is correct? RAID0 takes approach 1 or approach2? On Mon, Mar 15, 2010 at 1:28 PM, Beolach <beolach@xxxxxxxxx> wrote: > On Sun, Mar 14, 2010 at 23:26, rj <ratnadeep@xxxxxxxxx> wrote: >> Hi, >> >> How does MD RAID0 layer support disks with different sizes? >> 1. Does it take the size of smallest disk and do the striping >> accordingly? This way there would be wastage of space in bigger >> disks. >> Or >> 2. Does it stripe across all the space of disks? This way, if striping >> is not possible for a disk because it has exhausted the space, >> striping will continue or remaining devices (although with >> compromising performance for these stripes because they have one disk >> less). >> >> What approach md chooses? Also, what approach is taken for RAID5 in such cases? >> > > MD RAID0 follows #2; 4/5/6 follow #1. From the man page for md: > > RAID0 > <snip> > If devices in the array are not all the same size, then once the small‐ > est device has been exhausted, the RAID0 driver starts collecting > chunks into smaller stripes that only span the drives which still have > remaining space. > > RAID1 > <snip> > All devices in a RAID1 array should be the same size. If they are not, > then only the amount of space available on the smallest device is used > (any extra space on other devices is wasted). > <snip> > > RAID4 > <snip> > Unlike RAID0, RAID4 also requires that all stripes span all drives, so > extra space on devices that are larger than the smallest is wasted. > <snip> > > My understanding is that this is why MD RAID0 does not yet support > --grow, while MD RAID456 does - since they take different striping > approaches, it's much harder to reuse the --grow algorithm. > > > Good luck, > Conway S. Smith > -- 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
