[mythtv] Problems with using LVM for large storage
Neale Swinnerton
mythtv-dev.spam at isismanor.com
Mon May 16 00:04:11 UTC 2005
Why is this a surprise? You have one logical drive composed of multiple
physical drives and a bit of it fails. This would be the same if you had
one physical drive.
Why not use RAID-{1|5} drives as the PV's in your LVM volume group ?
with two disks you could arrange, using software raid, to have each PV
mirrored.
Eric Thelin wrote:
> I have been using myth with three drives in an LVM array running XFS. I
> just found out about the disadvantage of LVM. One of my drives failed.
> This caused a total loss of the array. This really got me thinking about
> the problems caused by myth's requirement that all recordings are put in
> the same directory. I know the official solution to growing beyond one
> drive is to use LVM to make one giant virtual drive. But I haven't heard
> or thought much about the down side that every drive you add to that array
> reduces the reliability of the entire volume. I would much rather see a
> situation where a failing drive only takes its portion of the total
> storage with it.
>
> But this is the developer
> list so I am not here to complain without proposing solutions. I have a
> few ideas. First, for the short term I have written a simple script that
> moves all recordings from the primary record directory to another drive
> (chosen at random from a list) and creates a symlink in the original
> location. For safty sake it waits until the file hasn't been modified
> for four hours to let scheduled jobs finish. There are more advanced ways
> to make sure myth is done writting the file but this will do for now. If
> anyone knows of any weakness with this concept please let me know. Once I
> test this a little more and give this opportunity for feedback I plan
> submit it for inclusion in the contrib directory. The better solution
> seems to be to make myth capable of handling multiple record directories.
> This would also allow us to simplify the installation by removing the
> reliance on LVM for large scale installs. We could either implement the
> same type of solution as my perl script or full handling of the multiple
> paths. If we add a field to the recorded table to store the destination
> path and modify all routines that read or write the files directly to use
> that complete path.
>
> I will submit my move script either in its current incarnation or as a
> script to be run as a user job to be run automaticly.
>
> Eric
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