[mythtv-users] Raid configurations

[Gregory Gee]

   Sorry to sound like a newbie here, but is there somewhere I could find
good instructions on setting up Raid5 with XFS?  I also have FC2 and
a TX4 and having looking around for setup options.

Thanks,
Greg

Terrence Martin wrote:
> Far from having performance issues you will find performance to be very 
> nice indeed.
> 
> I run this for my storage array at home. Here is my config.
> 
> FC2 + Promise 150TX4 SATA controller + 4x Seagate 160GB SATA Drives + 
> PIII 800Mhz + 2.6 Kernel + XFS
> 
> I just ran a test.
> 
> 52MB/s read, 33MB/s write
> 
> Definitely not performance to sneeze at for a $60 SATA controller and a 
> 3 year old computer. Particular on writes since raid5 is not know for 
> its write speed. The Linux kernel has a very fast RAID5 implementation.
> 
> My tests are done with a simple dd command
> 
> #Write test
> time dd if=/dev/zero of=bigfile.zero count=1000000 bs=1024
> sync
> # Read test
> time dd if=/dev/bigfile.zero of=/dev/null
> 
> Then I do some quick bc math.
> 
> I think this is a pretty good test for myth since this is similar to 
> what you expect for video, long multi gigabyte reads and writes. My 
> tests are 1GB which is approx 3 times RAM so disk cache effects would be 
> minimal.
> 
> 33MB/s will give you plenty of head room for multiple tuners.
> 
> A word of caution. RAID5 is the most disk efficient of the RAID 
> personalities. However it is also more risky that a true data mirror. 
> There is a non-zero chance that when you go to rebuild your array after 
> a disk failure that one of your other disks could fail during that very 
> intensive and time consuming process. I have first hand experience with 
> this sort of thing on a much more expensive hardware array (4.8TB 
> gone...:( ). If you can when a drive fails copy the data onto another 
> disk or some other backup. Then rebuild the array with the new drive. 
> Better to be safe than sorry.
> 
> Also if you have a unclean shutdown the array will take several hours to 
> re-initialize itself. During this time you will get reduced performance 
> during this initialization phase, although linux throttles this process 
> to 10MB/s.  This is different than a fsck (ext2) and file system type 
> does not effect it. It is simply a requirement in raid5 on unclean 
> shutdown to scan every block and test the parity.
> 
> Those caveats aside I have run RAID5 for many years both at work and at 
> home and it is a good compromise between data security, cost and 
> performance. I have lost 3 disks over the last 3 years but not one bit 
> of data.
> 
> On the disks, it is less space but if you get 4x200GB seagates ($131 ea 
> at newegg.com) you get 5 years of warranty. You may only get 1 with the 
> western digital. Also the Seagate are native SATA drives. We have pretty 
> much switched to seagate for all of our cluster nodes where possible. 
> Too much hassle with WD and Maxtor.
> 
> Terrence
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