Date: Tue, 23 Jul 2002 22:13:47 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Mark W. Krentel" <krentel@dreamscape.com> Cc: freebsd-stable@FreeBSD.ORG Subject: Re: 4.6-RC: Glacial speed of dump backups Message-ID: <200207240513.g6O5Dljx025899@apollo.backplane.com> References: <200207240505.g6O550534455@dreamscape.com>
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:Matthew Dillon wrote:
:> The filesystem wasn't idle and you didn't sync, so of course dump
:> screwed up! It would probably screw up on a FreeBSD box too.
:
:What's not idle? The file system is mounted, but there are no writes
:to it during the dump. This and other tests run fine in Freebsd, even
:without syncs (but of course I'd use sync in a real application). In
:Linux, even a loop of "while true ; do sync ; sleep 1 ; done" run for
:20 minutes makes no difference.
:
:There is something very different between Linux and Freebsd here, I
:just don't know what it is.
:
:--Mark
A filesystem which you have just written to is not idle. You
have to sync a couple of times to be sure all the data's gotten
to the platter, or wait a sufficiently long enough that the
filesystem syncer comes along and does it for you (which would
be within 60 seconds for FreeBSD). This is an almost universal
trueism.
Now FreeBSD's dump program does in fact do a sync() itself,
right in its main(). This is probably why you didn't see the
problem w/ FreeBSD. If FreeBSD's dump program did not do that
sync() your test would probably not have worked.
If linux's sync() does not sync the filesystem then it's a bug in
linux's sync(). For Linux, just to make sure it's a synchronization
problem, try unmounting the filesystem and then dumping it while
it is unmounted. If that works then it sounds to me like Linux's
sync() command is broken. However, if even unmounting the filesystem
does not fix dump, then it sounds like a mismatch between the filesystem
and the dump program.
-Matt
Matthew Dillon
<dillon@backplane.com>
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