[CentOS] Looking for a life-save LVM Guru

Sat Feb 28 23:28:25 UTC 2015
James A. Peltier <jpeltier at sfu.ca>


----- Original Message -----
| On Fri, 27 Feb 2015 19:24:57 -0800
| John R Pierce <pierce at hogranch.com> wrote:
| > On 2/27/2015 4:52 PM, Khemara Lyn wrote:
| > >
| > > What is the right way to recover the remaining PVs left?
| > 
| > take a filing cabinet packed full of 10s of 1000s of files of 100s of
| > pages each,   with the index cards interleaved in the files, and
| > remove 1/4th of the pages in the folders, including some of the
| > indexes... and toss everything else on the floor...    this is what
| > you have.   3 out of 4 pages, semi-randomly with no idea whats what.
| 
| And this is why I don't like LVM to begin with. If one of the drives
| dies, you're screwed not only for the data on that drive, but even for
| data on remaining healthy drives.
| 
| I never really saw the point of LVM. Storing data on plain physical
| partitions, having an intelligent directory structure and a few wise
| well-placed symlinks across the drives can go a long way in having
| flexible storage, which is way more robust than LVM. With today's huge
| drive capacities, I really see no reason to adjust the sizes of
| partitions on-the-fly, and putting several TB of data in a single
| directory is just Bad Design to begin with.
| 
| That said, if you have a multi-TB amount of critical data while not
| having at least a simple RAID-1 backup, you are already standing in a
| big pile of sh*t just waiting to become obvious, regardless of LVM and
| stuff. Hardware fails, and storing data without a backup is just simply
| a disaster waiting to happen.
| 
| Best, :-)
| Marko
| 

This is not an LVM vs physical partitioning problem.  This is a system component failed and it wasn't being monitored and so now we're in deep doo-doo problem.  This problem also came to us after there were many attempts to recover the problem that were likely done incorrectly.  If the disk was still at least partially accessible (monitoring would have caught that) there would be increased chances of data recovery, although maybe not much better.

People who understand how to use the system do not suffer these problems.  LVM adds a bit of complexity for a bit of extra benefits.  You can't blame LVM for user error.  Not having monitoring in place or backups is a user problem, not an LVM one.

I have managed Petabytes worth of data on LVM and not suffered this sort of problem *knock on wood*, but I also know that I'm not immune to it.  I don't even use partitions for anything but system drives.  I use whole disk PV to avoid things like partition alignment issues.  Not a single bit of data loss in 7 years dealing with these servers either.  At least none that weren't user error. ;)

-- 
James A. Peltier
IT Services - Research Computing Group
Simon Fraser University - Burnaby Campus
Phone   : 778-782-6573
Fax     : 778-782-3045
E-Mail  : jpeltier at sfu.ca
Website : http://www.sfu.ca/itservices
Twitter : @sfu_rcg
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