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I would like to hear from people who have personal experience recovering crashed systems or data from crashed drives using lvm+ext3 and ext3. Which option is harder to recover from backup or to extract missing data?

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3 Answers 3

up vote 8 down vote accepted

When it comes to recovering data from a hosed disk or system, straight ext3 will be slightly easier than LVM+ext3, simply because it adds a bit of additional complexity and your recovery tools need to be LVM aware.

However, LVM gives you significantly increased flexibility and is nearly always justified in my opinion. It can also make backups a lot easier and more reliable (LVM snapshots are really handy for backup purposes).

Having dealt with both, I didn't think the slight added difficulty of LVM was enough to rule it out, and when you factor in the advantages of LVM. . . well, I generally won't build a box without LVM unless I have a really good reason.

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What about LVM stability? Have you ever a server which crashed because of problems with LVM? –  Kazimieras Aliulis May 4 '09 at 15:49
    
Technically, yes, but it wasn't LVM's fault. We had some Xen servers that were cranked down so only 128MB of RAM was available to the Xen Host/Hypervisor. When doing some major LVM changes, we exhausted the memory and crashed the box. Outside of that very specific circumstance, I've never had a problem with stability that I even suspected was LVM related. I build every box with LVM, from virtualization boxes, to huge Oracle RAC cluster setups. –  Christopher Cashell May 4 '09 at 18:45
    
Regarding stability: Once LVM is in place and configured, access to the LVs don't even go through the LVM code. They go through the device mapper. Run 'dmsetup table' to see some Neat Stuff about how it works. –  MikeyB May 7 '09 at 17:10

Easier with lvm+ext3 versus ext3 on a partition. Consider losing the LVM headers vs losing partition tables. The LVM headers are backed up on the root filesystem. The partition table is not backed up anywhere.

If you save a copy of the partition table manually, it is easy to replace. But if you must restore on a default setup with no special backups, you can restore LVM's backups of the metadata. The commands to do so might be strange and confusing, but you can find reference to them by doing websearches.

If the partition table is easy to guess but you don't have an actual backup of it, you're probably at about the same level of complexity as restoring LVM headers from the backups that it keeps on its own.

If you have LVM PV headers that are not corrupted, it is much easier to find your data versus finding it on partition tables. (If you have many devices).

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You can recover the LVM info, it is just a bit of a pain (well, perhaps things have improved in the past year or two). LVM is handy, and probably worth it, unless you are certain about your partitioning.

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