[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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