Date: Sat, 08 Dec 2001 15:51:34 +0100 From: "Roger 'Rocky' Vetterberg" <listsub@rambo.simx.org> To: Mike Meyer <mwm@mired.org> Cc: questions@FreeBSD.ORG Subject: Re: mount_mfs with softupdate generates panic Message-ID: <3C1228F6.9060106@rambo.simx.org> References: <15377.28085.155538.40480@guru.mired.org>
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Mike Meyer wrote: > Roger 'Rocky' Vetterberg <listsub@rambo.simx.org> types: [snip] >>I agree, the performance gained of using Soft Updates on a memory disk >>is probably small, but as I mentioned, this was done purely for >>performance, hence the noatime and async flags. >> > > Async is ignored if you turn on soft updates. Soft updates isn't > stupid - it realizes that if you've turned on soft udpates on the > filesystem, async is not only irrelevant, but dangerous. > > >>Im by no means a filesystem expert, but Soft Updates should improve >>performance on memory disks as well as regular harddrives, right? >> > > Not necessarily. Soft updates orders writes from the buffer cache to > the hard disk. If your memory disk is working properly, those writes > never happen, because the disk and the buffer cache are one and the > same thing. This makes sence. As said, Im no expert, but I was thinking in similar ways when I did this. Therefor, I was a bit surprised when I found the option to enable Soft Updates in the mfs man file, but since it was there I figured it would increase performance. I suppose that if the mfs uses the swap device, which is a "normal" harddrive, Soft Updates could be usefull when writing data to the swap, but it would do little or no good when it comes to writing to the mfs. Is this correct, or am I way off track here? > But yes, the system shouldn't panic you you mount your mfs disk async. Its not async that panics it, its Soft Updates. The mfs works just fine, both with or without async, as long as I leave out the -U flag. I have tried this on all machines I have access to and can afford to panic, and Soft Updates on mfs always seems to crash the system. People have replied to the posting and expressed similar experiences, with lockups or panics as results. Has anyone ever succesfully used the -U flag to mount_mfs, or is this a bug? -- R To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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