Re: LVM info - OTHER than HOWTO's
dsr@randomstring.org wrote:
>
>Here's why not:
>
>LVM is a kludge.
Not at all, no. LVM *as a concept* has been around for ages in a lot
of enterprise systems. The Linux implementation using device-mapper
works reasonably well and provides a lot of features that people use a
lot.
>That doesn't mean it isn't useful, but it does mean that it's
>rarely the best tool.
>
>LVM can increase the size of partitions by giving them more space on
>either an empty section of disk or another disk. Either way, you
>then need to increase the filesystem size on that partition,
>which is usually but not always doable. It does not grant any
>extra redundancy, so when you add an extra disk, you have
>increased your chances of hardware failure taking out data.
>
>LVM can snapshot a partition, so that you can back it up or
>go back in time. Doing so is more complex, hairy, and
>time-consuming in LVM than in most alternatives, and should
>usually be avoided.
>
>LVM can do RAID mirroring, but not as well as mdadm RAID1 or 10.
>
>LVM can do RAID striping, but not as well as mdadm RAID0 or 10.
>
>LVM can do RAID5 or 6, but it takes more thought than with
>mdadm, and most people should avoid RAID5 or 6 most of the time.
>
>If you need to move things around once in a while, having a nice
>big disk available to use as a spare and copying things with
>rsync and dd is going to be easier.
>
>If you need to move things around a lot, you might want btrfs or
>zfs instead of lvm.
>
>If you don't need to move things around much, but just want
>performance, mdadm is better.
Or, do what lots of people do: use mdadm to provide the redundancy /
striping at the disk level, then use LVM on top of the mdadm-provided
RAID devices to give the flexibility with snapshots, flexible
partitioning, etc. As/when you need to migrate data, vgextend and
pvmove are massively useful tools. In my experience, pvmove makes a
huge difference - you can move data at ~raw disk speed from old disks
to new without downtime.
To Richard: LVM is never going to work with a dual-boot system unless
you're hosting that system virtually under Linux. It's just like
Windows' own multi-disc flexible storage stuff isn't going to work
with anybody else. If that's an issue for you, then either stay away
from LVM or make sure you have some spare space that's available for
sharing between the different OSes using a common filesystem.
--
Steve McIntyre, Cambridge, UK. steve@einval.com
"Further comment on how I feel about IBM will appear once I've worked out
whether they're being malicious or incompetent. Capital letters are forecast."
Matthew Garrett, http://www.livejournal.com/users/mjg59/30675.html
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