Date: Sun, 15 Jun 2008 03:08:34 +0200 From: Kris Kennaway <kris@FreeBSD.org> To: RW <fbsd06@mlists.homeunix.com> Cc: freebsd-questions@freebsd.org Subject: Re: md devices mounted with async Message-ID: <48546B92.5050906@FreeBSD.org> In-Reply-To: <20080615013158.7dd19cf0@gumby.homeunix.com.> References: <20080614224742.17316919@gumby.homeunix.com.> <48545212.4040006@FreeBSD.org> <20080615013158.7dd19cf0@gumby.homeunix.com.>
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RW wrote: > On Sun, 15 Jun 2008 01:19:46 +0200 > Kris Kennaway <kris@FreeBSD.org> wrote: > >> RW wrote: >>> mdmfs(8) has an example of a malloc-backed md device mounted with >>> the async option. Is there any point in doing this with malloc and >>> vnode devices? In neither case does a write to the file-system >>> require a write to a physical disk. >> Well, for vnode devices it does write to the disk, > > I meant that a write to the filesystem doesn't require a corresponding > write to disk, and the change can stay in memory indefinitely. > Presumably, more or less, the same inactive pages get written-out to > swap, with or without async. Well, it doesn't necessarily cause a write to disk for each filesystem write, but the synchronization mode of the filesystem to the backing store is precisely what the async/noasync/sync mount options control! >> but that isn't the >> point; in both cases you are writing to the filesystem that is >> mounted on top of the md, so that will be faster if it is mounted >> async. > > In that case, why doesn't /etc/rc.d/tmp default to mounting its > swap-backed /tmp with async? It should. Kris
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