Date: Fri, 23 Jun 2000 07:52:44 +1000 From: Peter Jeremy <peter.jeremy@alcatel.com.au> To: Chris Dillon <cdillon@wolves.k12.mo.us> Cc: cvs-all@FreeBSD.ORG, current@FreeBSD.ORG Subject: Re: cvs commit: src/sys/contrib/softupdates softdep.h ffs_softdep.c Message-ID: <00Jun23.075254est.115312@border.alcanet.com.au> In-Reply-To: <Pine.BSF.4.20.0006221513300.6657-100000@mail.wolves.k12.mo.us>; from cdillon@wolves.k12.mo.us on Thu, Jun 22, 2000 at 03:22:12PM -0500 References: <86g0q6gw5x.wl@localhost.local.idaemons.org> <Pine.BSF.4.20.0006221513300.6657-100000@mail.wolves.k12.mo.us>
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On 2000-Jun-22 15:22:12 -0500, Chris Dillon <cdillon@wolves.k12.mo.us> wrote: >I think it would be a very good idea to enable softupdates by default >when a new filesystem is created. Modify newfs to do this and use >tunefs only if you want to _disable_ softupdates on a filesystem. My only concern with doing this is softupdates behaviour when disk space is freed. If you delete a file, it takes about 20 seconds for the space occupied by the file to appear in the free list. If you have relatively little free disk space and write another file, you can get `disk full', even though there will be sufficient free space when the freed blocks become available. This has bitten a number of people who have turned softupdates on for their root filesystems - and had installworld die. Whilst the solution to this appears obvious (if you can't allocate a block, but there are free blocks on the to-be-commited list, wait for free space to become available), actually implementing it is quite difficult if you want to avoid deadlocks. Kirk has previously recommended that softupdates not be enabled on a filesystem unless it has sufficient free space to absorb about 1 minute's writes. A number of people have also claimed that softupdates interacts with Vinum (particularly RAID-5) in undesirable ways. I believe that at least some of this was a misunderstanding of the way softupdates handles write re-ordering (or at least the write semantics that softupdates expects). Peter To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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