swap at beginning of slice - danger?
Dmitry Pryanishnikov
dmitry at atlantis.dp.ua
Wed Mar 15 12:53:20 UTC 2006
Hello!
On Wed, 15 Mar 2006, Vadim Goncharov wrote:
> I have 5.5-PRERELEASE server in production, booting from ad0s1:
>
> # BLOCKSIZE=512 swapinfo
> Device 512-blocks Used Avail Capacity
> /dev/ad0s1b 2097152 52872 2044280 3%
> /dev/ad1s1b 2097152 51952 2045200 2%
> Total 4194304 104824 4089480 2%
> # bsdlabel ad0s1 | fgrep b:
> b: 2097152 0 swap
>
> Previously, on a 4.11 system, swapinfo said that swap size was less than
> size of b: partition on a slice - it was ok, as boot sectors are
> located at beginning of slice. But now, sizes match exactly. What
> changed and is it dangerous nowadays to have swap partition at offset 0 ?
It seems to me as a dangerous setup indeed - swap could easily overwrite
disklabel (which is in sector 1 of the slice for every arch except Alpha). FFS
doesn't touch first several sectors, so it would be safe to start FFS
partition from the offset 0, but AFAIK swap engine makes no such guaranties. I
don't know about current situation in RELENG_5, but in CURRENT bsdlabel by
default reserves first 16 sectors for the disklabel, so offset of the first
partition will be 16 regardless of the partition type. But stupid sysinstall
still insists on putting first partition at offset 0, and it's a shame. For
production server I would deactivate swap on this disk and recreate
b-partition in order to start at offset 16, not 0.
Sincerely, Dmitry
--
Atlantis ISP, System Administrator
e-mail: dmitry at atlantis.dp.ua
nic-hdl: LYNX-RIPE
More information about the freebsd-stable
mailing list