RFC: swap on a LVM volume in debian-installer
Hi all,
in debian-installer, there is a package - partman-auto-lvm - which can
setup an entire disk to be used for the debian installation with the use
of lvm for most partitions.
Currently it sets up one boot partition, one swap partition and one lvm
PV which is used for the rest of the partitions (usually root and
possibly home depending on the recipe used).
I'm currently considering whether to change partman-auto-lvm so that the
swap partition is created as a lvm lv rather than a separate partition,
and I'd like to ask for some comments and feedback before doing so.
The last discussion of this feature seems to have been in this thread:
http://lists.debian.org/debian-boot/2005/10/msg00842.html
===
So far, I've seen the following advantages and disadvantages of
swap-on-lvm mentioned:
Advantages
==========
o makes more partitions available to LVM
This means that the swap space can also be managed via the regular lvm
tools. Swap space can be reclaimed, enlarged and shrunk using the
regular tools when needed. E.g. if a larger swap space is needed, one can
do a swapoff, lvextend, mkswap, swapon. In general, to get the most out
of lvm, as many partitions as possible should use it.
Disadvantages
=============
These are mostly gathered from the above thread:
o lowmem
I'm not sure this is an issue. If root is already accessed via lvm, will
accessing swap via lvm make a difference in lowmem situations?
o suspend-to-disk
There have been concerns that suspend/resume may not work with swap on a
lvm volume.
Using initramfs-tools, it seems perfectly possible to resume from a swap
partition on lvm (I do so daily). I am not sure whether yaird supports
this feature.
o overhead
Accessing swap via the LVM layer might introduce additional overhead.
However, the LVM maintainer disagreed in the above thread, noting that
swap should be an io-bound operation and I tend to agree.
Note that these disadvantages might be i386 oriented, are there any
other disadvantages on other arches, or on i386 for that matter, that
I've overlooked?
Discussion of additional advantages would also be welcome of course :)
===
The reason that I'm personally interested is that swap-on-lvm as the
default for a lvm install would allow the experimental partman-auto-crypto
(a package which uses partman-crypto and partman-auto-lvm to
automatically partition a disk so that any partition except /boot will
be encrypted) to share 90% of its code with partman-auto-lvm.
Comments welcome.
Regards,
David
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