For Lenny: LVM, LVM+MD or just MD for mirroring?
Hi everybody,
I am a long term Debian user (since 1996, actually). I am about to set
up
a new debian server using Lenny, which will go into production
probably in
October. This machine will use lighttpd, mysql, dovecot/postfix among
others.
Currently I use two harddisks and MD for all servers to guard against
harddisk failure, and to gain additional read speed. For the new
machine,
I would like to try LVM2 but after spending a week browsing Google and
news articles, I am a bit confused.
There are two things I want to achieve:
1. guard against harddisk failure, get notified (by mail / SMS /
whateveR)
when one fails
MD does this beautifully and my current server has had a few harddisk
failures which were all handled very well.
2. [NEW] do backups using snapshots, to minimize downtime for backups.
I have read LVM2 does this very well, currently I have to shutdown
everything for backups (nightly), which basically sucks.
I do NOT need dynamic resizing of partitions.
My current server is (still) an updated Sarge installation , running
since
Sarge was "testing", and it has never felt the need to add space. I
will
have two 400GB disks in the new machine which will be far more than I
need
(currently I have 2x160GB of which 75GB are used).
I would like something like the following setup:
10GB root, 2GB swap, 4GB tmp, 10GB /var, and the rest for data. All
mirrored 1:1 on both disks.
If possible, I would like to use a stock kernel (no self-compiles) and
stock Debian utilities, to ease upgrades.
Questions:
-- Generally: Is it a good idea to use LVM2 mirroring or should I
stick to
MD for mirroring, and use LVM only for the snapshots? This seems
overcomplicated.
-- Can Lenny create and use mirrored LVM partitions? I tried a test
installation in VMware but the installer does not offer a mirroring
feature, only
encryption.
-- Can Lenny's boot manager install itself on both mirrored harddisks'
MBRs and boot from both?
-- Can Lenny boot from a LVM2 logical volume?
-- Lenny does not seem to contain 'dmeventd', which (I heard) is
necessary
to detect disk failures and deactivate failed mirrors, like 'mdadm'
did
with 'md'. Can it, or should it, be added, or is there an alternative
way
of doing this?
Generally I would like to hear any experiences with LVM2 you can
offer.
The last time I tried LVM I hosed everything, but that was eight years
ago, at least partly due to a user error, and with LVM1 on Debian
Woody
with a self-compiled kernel on 2.4.2x.
Thank you!
Jens
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