Date: Tue, 11 Jan 2000 17:41:59 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Alexey Zelkin <phantom@cris.net> Cc: current@FreeBSD.ORG Subject: Re: vn device strange behaviour Message-ID: <200001120141.RAA65875@apollo.backplane.com> References: <20000112013234.A28567@scorpion.crimea.ua>
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:hi,
:
:I just discovered some strange points about using vn devices (files) as
:swap devices.
:
:I have placed below some output gathered with script(1) and now
:some comments.
:
:1) I can easy unconfigure vn device which already mounted as swap device
:and then remove swapfile without any problems. I not sure about behaviour
:of the swapper when it will try to allocate swap from /dev/vn0c.
:
:2) When I am creating small file (about 100k) and try to mount it as swap
:device swapinfo(8) output looks broken.
:
:3) I could not mount three and more vn devices as swap devices.
:
:BTW, I also got strange results once (but I could not reporoduce it later):
:swapinfo(8) shown that I have three swap devices mounted: /dev/wd0s1b,
:/dev/rvn0c and /dev/#46:10. What's that ? I'll try to reproduce it again,
:but ...
:
:Comments ?
Don't unconfigure a VN device mounted as swap unless you want your
system to die a horrible death. It shouldn't allow it to happen, but
it does and that's a bug.
The first 128K of any swap partition is left alone by the swap subsystem
in order to ensure that the disklabel (if any) is not overwritten. Do
not configure tiny swap spaces -- apart from being useless they will
cause swapinfo to print confusing output.
By default the kernel is configured to support 4 SWAP partitions.
Therefore you can only configure a maximum of 4 SWAP partiions. You
can change this in the kernel config. Note however that setting the
number arbitrarily high will cause a huge amount of KVM to be wasted.
Four is usually enough for anyone.
At some point in the future it will be possible to unconfigure swap,
but not right now.
-Matt
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