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Questions[lvm](server)

Martin Hope
nip3o
Asked: 2011-08-15 04:50:09 +0800 CST
  • 34

As far as I know, LVM makes it possible to take snapshots of a volume. There are also a number of file systems (ZFS, Btrfs, reiserfs, ...) which supports snapshots.

However, I've never understood the difference between LVM snapshots and file system snapshots. If it's possible to take snapshots with LVM, why does someone take their time to implement it in a file system?

Edit: Is any of them preferred in some situations? Why?

lvm snapshot zfs btrfs
Martin Hope
Ency
Asked: 2011-01-01 04:55:36 +0800 CST
  • 54

I currently have LVM on software RAID, but I'd like to ask you what you think it is better solution, maybe some pros and cons?

Edit: It is about software raid on lvm or lvm on software raid. I know than hardware raid is better if we are thinking about performance.

linux lvm raid software-raid
Martin Hope
jens
Asked: 2010-12-06 22:02:42 +0800 CST
  • 32

I would be thankfull if someone who understands how LVM works, could tell me a rough estimate, how much slower using LVM (with a Software RAID1) will be.

(What I do not want to know how much slower LVM will be if the LVM Volume is currently in snapshot mode doing Copy on Write). I only need some rough estmiate how much LVM will slow down reads and writes in a normal operation scenario.

Any links are also very much appreciated I was not able to find any good performance benachmarks about this question.

performance lvm
Martin Hope
Sandra
Asked: 2010-08-15 12:17:10 +0800 CST
  • 33

I connect an iSCSI target, create a Physical Volume and Volume Group on it.

Then I create an LV, and

mkfs.ext3 /dev/vg00/vm

and all that works great.

Then I disconnect the target

iscsiadm -m node -T iqn.2004-04.com.qnap:ts-509:iscsi.linux01.ba4731 -p 192.168.0.4 -u

login to another Linux server, and connect the target there

iscsiadm -m node -T iqn.2004-04.com.qnap:ts-509:iscsi.linux01.ba4731 -p 192.168.0.4 -l

and I get:

linux01:~ # lvdisplay 
  --- Logical volume ---
  LV Name                /dev/vg00/vm
  VG Name                vg00
  LV UUID                NBNRGV-FkSR-ZNZ9-9AVk-chLQ-j5nc-RazeBw
  LV Write Access        read/write
  LV Status              NOT available
      LV Size                17.00 GB
  Current LE             4352
  Segments               1
  Allocation             inherit
  Read ahead sectors     0

I can see that /dev/vg00/vm doesn't exist, as I would have expected.

What am I doing wrong?

linux lvm iscsi