Linked by Thom Holwerda on Tue 10th Mar 2009 15:05 UTC, submitted by vijayd81
Linux In Linux distros, how do you know how much space to assign for each partition? And what if you do this and then later run out of room? Well you could delete data or move it off to other partitions, but there is a much more powerful and flexible way. It's called Logical Volume Management. LVM is a way to dynamically create, delete, re-size and expand partitions on your computer. It's not just for servers, it's great for desktops too! How does it work? Instead of your partition information residing on your partition table, LVM writes its own information separately and keeps track of where partitions are, what devices are a part of them and how big they are.
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ephemient
Member since:
2009-03-11

ext3 and xfs are a bit slower on LVM, because LVM doesn't support barriers. Also there are cases when xfs stacked atop LVM stacked atop other drivers can overflow x86's 4kB kernel stack. It's also possible to make a mess of the mappings, so the logical block numbers of the virtual device are randomly scattered across the physical devices. That takes quite a bit of effort to achieve, though ;)

What we call LVM these days is actually LVM2, built on top of Linux 2.6's device-mapper (LVM1 is Linux 2.4's volume manager). EVMS used to be a nice front-end to LVM, but is kinda unmaintained nowadays. mdadm handles RAID, which you might think would be part of volume management, but dm only supports RAID-1 for now.

Going proprietary, VxVM (Veritas Volume Manager) is available for Linux too. I have no idea how it compares.

Reply Parent Score: 1

giddie Member since:
2008-04-29

The way I understand it, the fact that LVM doesn't honour write barriers doesn't have any bearing on performance. However, it does mean that journalling filesystems aren't 100% protected from corruption after power cuts.

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ephemient Member since:
2009-03-11

My recollection was wrong -- it seems that when barriers are turned off, Linux filesystems act unsafely instead of simulating barriers with flushes and waits. So the lack of barriers actually improves performance.

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josi Member since:
2009-03-11

Mandriva's diskdrake support both LVM and RAID.

OpenSuse's yast support LVM and I suppose also RAID.

When you choose distro, you should look for more than just browser plugins and a nice theme...

Reply Parent Score: 1

ephemient Member since:
2009-03-11

Every enterprise distribution supports LVM on top of mdadm RAID these days -- Debian's installer partitioner supports it, as does Fedora's and RHEL's.

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