} -----Original Message----- } From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid- } owner@xxxxxxxxxxxxxxx] On Behalf Of Neil Brown } Sent: Sunday, April 30, 2006 12:13 AM } To: Molle Bestefich } Cc: linux-raid@xxxxxxxxxxxxxxx } Subject: Re: [PATCH 003 of 5] md: Change ENOTSUPP to EOPNOTSUPP } } On Friday April 28, molle.bestefich@xxxxxxxxx wrote: } > NeilBrown wrote: } > > Change ENOTSUPP to EOPNOTSUPP } > > Because that is what you get if a BIO_RW_BARRIER isn't supported ! } > } > Dumb question, hope someone can answer it :). } > } > Does this mean that any version of MD up till now won't know that SATA } > disks does not support barriers, and therefore won't flush SATA disks } > and therefore I need to disable the disks's write cache if I want to } > be 100% sure that raid arrays are not corrupted? } > } > Or am I way off :-). } } The effect of this bug is almost unnoticeable. } } In almost all cases, md will detect that a drive doesn't support } barriers when writing out the superblock - this is completely separate } code and is correct. Thus md/raid1 will reject any barrier requests } coming from the filesystem and will never pass them down, and will not } make a wrong decision because of this bug. } } The only cases where this bug could cause a problem are: } 1/ when the first write is a barrier write. It is possible that } reiserfs does this in some cases. However only this write will be } at risk. } 2/ if a device changes its behaviour from accepting barriers to } not accepting barrier (Which is very uncommon). } } As md will be rejecting barrier requests, the filesystem will know not } to trust them and should use other techniques such as waiting for } dependant requests to complete, and calling blkdev_issue_flush were } appropriate. } } Whether filesystems actually do this, I am less certain. What if a disk is hot added while the filesystem is mounted. And the new disk does not support barriers but the old disks do? Or you have a mix? If the new disk can't be handled correctly, maybe md should refuse to add it. Guy } } 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 - 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
