lvm and server install

[unre4l]

Are there any advantages to using lvm2 on say a app server or db server where all data is stored in the san. Is the major advantage of lvm ease in changing volume or partition sizes?
Just trying to figure out if we would need it for any reason on a server where actual data on the server itself does not change much.
Thanks.

[Ivan Ferreira]

LVM provides you flexibility. Even if the Data is on the SAN, what would you do if you need more space in one file system? With LVM you can add more luns to the volume group and extend the logical volume.

You can also use the snapshot features that allows you to minimize the time of db down for backups.

[unre4l]

I am not too faimilar with how the LUNs work with the EVAs but once a LUN is created, isn't there something that you can do within the management interface to expand it without having to deal with LVM's and such??

As far as backups are concerned we do online backups so thats not a concern.

[Ivan Ferreira]

>>> I am not too faimilar with how the LUNs work with the EVAs but once a LUN is created, isn't there something that you can do within the management interface to expand it without having to deal with LVM's and such??

No. Even when you can extend the size of a LUN in the EVA, you can't tell to linux that the underlying disk was resized. The Linux OS will still see the old disk geometry.

If you want to increase the size of a Disk in Linux on a SAN based configuration, you create another VDISK in the storage, present it to Linux, add the disk to the LVM volume group and the size of the volume group is extended. Then you can extend the logical volume and the file system size.

[unre4l]

Hi Ivan
I was trying to find something more about the topic and ran into this thread
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=1100408

The guys says that when he changed tghe lun size and did a reboot linux was able to see the new size. The downside is the reboot but thats not a big deal as these sort of things will happen only during a planned downtime. I guess lvm gives more flexibility but even without it if you increase the lun size and rebooted the box it should work?

[Steven E. Protter]

Shalom,

I like lvm for two reasons:

1) As noted above flexibility.
2) The commands are the same as HP-UX lvm to a great degree and I've got a lot of time on that platform.

SEP

[Ivan Ferreira · Accepted solution]

Even if you reboot, the new lun size won't be seen, you need to update the disk partition table.

In Tru64, you can do this with disklabel -rw, but linux does not provides a functionality like that.

Why are you refusing to use LVM?

[Court Campbell]

Do not fear lvm. It is awesome. You can expand logical volumes and filesystems on the fly. You can stripe, mirror, etc. lvm seems strange at first, but when you use it and see how much time it saves, you'll love it. check out the Red Hat lvm admin guide:

https://www.redhat.com/docs/manuals/enterprise/RHEL-5-manual/Cluster_Logical_Volume_Manager/index.html

I also use lvm on HP-UX, but I like the linux implementation better.

[unre4l]

I am not averse to lvm. Just wanted to know what the compelling reasons were to use it and especially in a environment where the server itself has data that changes very little. It does have its advantages and if it does not add any overhead then it might be very handy. Thanks.