On 9/25/2013 4:34 PM, Chris Murphy wrote: > > On Sep 25, 2013, at 3:18 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote: > >> On 9/25/2013 7:56 AM, Stewart Webb wrote: >>> Hi All, >> >> Hi Stewart, >> >>> I am trying to do the following: >>> 3 x Hardware RAID Cards each with a raid 6 volume of 12 disks presented to >>> the OS >>> all raid units have a "stripe size" of 512 KB >> >> Just for future reference so you're using correct terminology, a value >> of 512KB is surely your XFS su value, also called a "strip" in LSI >> terminology, or a "chunk" in Linux software md/RAID terminology. This >> is the amount of data written to each data spindle (excluding parity) in >> the array. >> >> "Stripe size" is a synonym of XFS sw, which is su * #disks. This is the >> amount of data written across the full RAID stripe (excluding parity). >> >>> so given the info on the xfs.org wiki - I sould give each filesystem a >>> sunit of 512 KB and a swidth of 10 (because RAID 6 has 2 parity disks) >> >> Partially correct. If you format each /dev/[device] presented by the >> RAID controller with an XFS filesystem, 3 filesystems total, then your >> values above are correct. EXCEPT you must use the su/sw parameters in >> mkfs.xfs if using BYTE values. See mkfs.xfs(8) Small correction: su is a byte value. sw is an integer representing the number of data spindles. >>> all well and good >>> >>> But - I would like to use Linear LVM to bring all 3 cards into 1 logical >>> volume - >>> here is where my question crops up: >>> Does this effect how I need to align the filesystem? >> >> In the case of a concatenation, which is what LVM linear is, you should >> use an XFS alignment identical to that for a single array as above. > > So keeping the example, 3 arrays x 10 data disks, would this be su=512k and sw=30? No. In this configuration, as far as XFS is concerned LVM doesn't exist in the stack because it doesn't change the RAID geometry, so you ignore it. -- Stan _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
