[mythtv-users] INFO: RAID comparison for MythTV

Allan Stirling Dibblahmythml0015 at pendor.org
Thu Apr 21 20:00:02 UTC 2005

MagicITX wrote:
> A week or so ago there was a thread discussing RAID for MythTV.  We
> did a test comparing software RAID 10 and RAID 5 on a mythbackend
> server. You can find the article on our site if you're interested. 
> Basically we found that the parity calculation for RAID 5 had a
> minimal impact on the performance of the system.  We did see much
> better throughput under RAID 10 as one would expect.
Not bad. However, you say 75% of the storage is available for data. This 
is incorrect.

I have a 9 drive raid5, with 200Gb drives. One is hotspare, leaving 8 
drives in the array. I have 1.4Tb of storage available.

As you increase the number of drives, the overhead of raid5 decreases - 
This applies to the CPU overhead for the parity stripe as well as the 
impact on storage available.

Also, more spindles == more performance, almost always. Going for 
smaller drives will get you more "bang for the buck" than larger, as 
long as you have plenty of controller ports available.

As another hint - Start your RAID small and grow it. Buying your disks 
all at once means that they'll all tend to fail at once - Which is not a 
good thing. Unfortunately, there's no easy, reliable way I've found to 
extend a RAID without backing up (somewhere really huge :) and restoring.



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