Lee Marzke on 15 Jul 2010 14:04:20 -0700

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Re: [PLUG] Laptop recovery--useful data to collect?--A tangent

On 07/14/2010 10:07 PM, Richard Freeman wrote:
On 07/14/2010 08:59 PM, Lee Marzke wrote:
Well for Ubuntu 10.04, you just boot from the CD rescue partition, and
then open the encrypted LVM, and fsck the disk. You may have to manually
search for the proper lvm device names ( lvscan, lvmdiskscan, vgscan, etc )

How robust is LVM with encryption? Is the amount of data lost during a power failure comparable to not using encryption? I imagine that it must encrypt each block separately, so that if there is some kind of interruption you only lose one block of disk.

I've used ext3 ( now ext4 ) on encrypted LVM (Ubuntu) for almost 4 years now on my laptop with no issues.

Ocassionally a hang due to sleep/hibernate failures typically get fsck'ed automatically ( for /home )
and only one time did I have to boot the install CD to manually fsck / )

That would be my main concern with it - if you can simply manually create the devices and fsck everything that isn't too big a deal. I just don't want one byte lost to result in half the drive getting scrambled.

I imagine that the concern with scrambling the disk is possible only during writes of disk meta-data, and with ext3 / ext4 that should be journaled. Otherwise only the file being written at the time would be subject
to corruption.

That seems to be my experience as well, I don't recall any issues after forcing a fsck.

Using a COW filesystem with built-in encryption would probably be a good move as well. You essentially get data=writeback on such a filesystem for free, which would probably help mitigate problems caused by errors at lower layers.



"Between subtle shading and the absence of light lies the nuance of iqlusion..."  - Kryptos

Lee Marzke,  lee@marzke.net   http://marzke.net/lee/
IT Consultant, VMware, VCenter, SAN storage, infrastructure, SW CM
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