[mythtv-users] EXT3 on Software RAID5 optimization

[Guillaume Laurès]

Le 3 sept. 08 à 17:50, James Skimming a écrit :

>> As I had some trouble on my recording storage (JFS/LVM2/RAID5), I
>> decided to recreate my storage with a ext3 fs on raid5 (mdadm).
>> I know that ext3 isn't the most efficient filesystem for this  
>> purpose,
> I
>> don't want to use JFS anymore and I also read some messages talking
>> about trouble with XFS.
>
> I'm sure if you search for it, you'll find someone who's had trouble
> with every file system.

True. I do have concerns with my XFS setup, but it's because I use it  
over NFS. Otherwise (I mean when directly attached to the mythtv box)  
it's a premium choice:
- fast,
- few fragmentation prone,
- excellent at taking care of underlaying raid stripes,
- good defragementer in case needed !

On my side I have two backends writing on one remote NFS share, which  
use XFS a underlying file system. I strongly advise against this kind  
of setup. Better attach the XFS filesytstem on one backend and then  
share it with NFS for the other(s).

The problem lies with block allocation. Something with NFS prevent XFS  
to do a good job and the file system gets awfully fragmented with only  
a few tens of recordings. It's a known problem of XFS when using NFS,  
and it seems not to have any solution.
I noticed that when starting this setup and I ran the defragmenter  
every night. But it's not available anymore now (the NFS server is  
openfiler) and after 6+ monthes when there's only 15% space left I  
feel the speed of the storage system getting really low. Perhaps I  
should delete/archive some recordings...


Just for fun:
"xfs_db -c frag -r /dev/data/nfs_mythtv" gives "actual 321943, ideal  
8142, fragmentation factor 97.47%"


Cheers,

GoM