Messages in this thread | | | Date | Mon, 12 Sep 2005 02:22:08 +0200 | From | Jesper Juhl <> | Subject | Re: read-from-all-disks support for RAID1? |
| |
On 9/12/05, Neil Brown <neilb@cse.unsw.edu.au> wrote: > On Saturday September 10, buytenh@wantstofly.org wrote: > > (please CC on replies) > > > > Hi! > > > > I recently had a case where one disk in a two-disk RAID1 array went > > subtly bad, effectively refusing to write to certain sectors without > > reporting an error. Basically, parts of the disk went undetectably > > read-only, causing file system corruption that wouldn't go away after > > fsck, and all kinds of other fun. > > That really isn't something that a drive should do. If a write fails, > you need to be told that it failed. If anything else happens, maybe > you should consider boycotting that manufacturer, or at least buying > more expensive drives (do I guess right that there were fairly > cheap??). > > > > > > Would it be hard/wise to add an option for RAID1 mode to read from all > > devices on a read, and report an error to syslog or simply return an > > I/O error if there is a mismatch? (Or use majority voting and tell > > people to use 3-disk RAID1 arrays from now on ;-) > > > > No, I don't think so. The overhead would be substantial, so people > would be very unlikely to use it.
There are situations where data integrity is far more important than speed. On AIX I usually use the Mirror Write Consistency and Write Verify options on my mirrored volumes that store data where integrity is more important than speed. I guess something like those options would also satisfy Lennert's needs, but I don't know if it's currently possible with the Linux LVM or elsewhere.
You can read a bit about the MWC and WV options in AIX at : http://publib.boulder.ibm.com/infocenter/pseries/index.jsp?topic=/com.ibm.aix.doc/aixbman/prftungd/diskperf2.htm
-- Jesper Juhl <jesper.juhl@gmail.com> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |