[mythtv-users] Problems with External USB Drives

[R. G. Newbury]

Jonno wrote:
> Hi,
> 
> I'm running Mythbuntu 8.04 with an external 750GB USB drive to store
> my recordings. I've had various problems over the past year with the
> external drives. First the power brick failed and now the drive just
> seems to be locking up after a short while of working.
> I thought overfilling the drive might be an issue so I set the "free
> space" in myth to 5GB thinking it would be plenty. However it is now
> locking up before 24hrs have gone by. It always works for a short
> while after I restart. I don't know how to debug this. Is there a way
> in Myth to monitor the drive temp while it is being used? It doesn't
> feel too hot but I can't think what else to check. Do you think 5GB
> free space is enough on a 750GB drive? Anything else to look for?

AIUI the 'free space' is a hard limit amount of space which myth will 
not touch, so that you can use it for *other* stuff. It's mainly 
intended for drives where your OS *and* filesystem are on the same 
partition. Myth then leaves the space for the OS to use for log files 
etc. It's a real head-scratcher to have your system crash for no obvious 
  reason (when you forget to check that the log files have filled the 
partition!).

In your case, that does not apply. You are just reducing the available 
storage space. Try checking the fragmentation of the drive. And if it 
turns out to be heavily fragmented, which is quite possible if you have 
used it for some time, consider changing to a different file system and 
changing the allocation size.

xfs and jfs have advantages over ext3 for our type of filesystem use, 
not the least of which is that deletes don't lock up the drive. I can't 
remember *why* I chose xfs over jfs but it works for me!

I use xfs only on my video drives. A fragmentation check showed that the 
older drive, a 250G with 2 years of use, had a 97% fragmentation level!
I 'defragged' (it dropped to 2%) and changed the file 'chunk' allocation 
to  1 Gig.

I probably went too far with that, 250M would probably be better. I do 
not know the default allocation size but I am sure that it is nowhere 
near 250M!

The file size allocation is the amount of space the filesystem allocates 
  in one chunk, when the OS asks for some storage space. For standard 
definition files running about 2.3Gig per hour, a 1 Gig allocation is 
probably too large and wastes some space. Not so much waste for HD files 
averaging 8G per hour, though. YMMV.

Geoff


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