Date: Sat, 20 May 2000 12:49:37 +0930 From: Greg Lehey <grog@lemis.com> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Matthew Reimer <mreimer@vpop.net>, current@FreeBSD.ORG Subject: Re: Possible Vinum RAID-5 problems? (was: panic: ffs_valloc: dup alloc) Message-ID: <20000520124936.E57670@freebie.lemis.com> In-Reply-To: <200005191943.MAA40388@apollo.backplane.com> References: <lists.freebsd.current.20000519075536.A31215@cicely5.cicely.de> <lists.freebsd.current.20000519182044.A47558@freebie.lemis.com> <39256530.1FD33AA5@vpop.net> <200005191943.MAA40388@apollo.backplane.com>
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On Friday, 19 May 2000 at 12:43:28 -0700, Matthew Dillon wrote: > >> Greg Lehey wrote: >>> >>> As far as soft updates goes, basically it's incompatible with Vinum, >>> since there's currently no way of ensuring the sequence of writes >>> across a number of disks. I'm thinking of ways of doing it, but they >>> will cause significant loss in performance. There should be no >>> problems as long as there isn't a crash, of course :-) >> >> Do you mean that softupdates is entirely incompatible with Vinum, or >> just incompatible with Vinum's RAID5? > > Wait a sec... softupdates does not depend on write ordering. > Softupdates issues all non-conflicting writes in parallel and > doesn't care what order they are written to the disk. When > those complete, softupdates will then followup with all the > writes that depend on the original set. Hmm. Maybe I've misunderstood, then. It was my understanding that soft updates writes metadata with WRITE_ORDERED set, and thus avoids having to explicitly wait for completion. It's the WRITE_ORDERED that Vinum doesn't handle correctly. On a single disk, it's just a question of not sorting around a WRITE_ORDERED request. Vinum will keep the WRITE_ORDERED on a single disk, but it won't ensure that a request for the same volume, but which is destined for a different disk, will not be written until after all components of a prior WRITE_ORDERED request for that volume. Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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