[ ... ] > Back to the original issue. Coolcold and I were trying to > figure out what the XFS write stripe alignment should be for a > 7 disk mdraid10 near layout array. After multiple posts from > David, Robin, and Keld attempting to 'educate' me WRT the > mdraid driver read tricks which yield an "effective RAID0 > stripe", nobody has yet answered my question: > What is the stripe spindle width of a 7 drive mdraid near array? As I have repeated many many many times to you in past XFS discussions, and please take note, stripe alignment matters ONLY AND SOLELY IF READ-MODIFY-WRITE is involved, and RADI10 never requires read-modify-write. > Do note that stripe width is specific to writes. It has > nothing to do with reads, from the filesystem perspective > anyway. For internal array operations it will. Again, stripe alignment only matters for writes ONLY AND SOLELY IF READ-MODIFY-WRITE is involved. This never happens for RAID0, RAID1 or RAID10, because there is no parity to update; chunks within a stripe are wholly independent of each other. Not all parity RAID involves read-modify-write either, for example RAID2 and RAID3 (bit and byte parallel parity RAID under the SNIA taxonomy) never do read-modify-write either, so stripe alignment does not matter for those either. Note: this is because RAID setups where the physical sector (bit or byte) is smaller than the logical sector always do whole-stripe reads or writes, which is a special case. Disclaimer: using stripe alignment even when it is not required may help a bit with scheduling, it being slightly akin to a larger block size, but not quite, but that is a secondary effect. -- 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
