[mythtv-users] OT-RAID 5 failure. MDADM experts? Seagate 1.5TB failure

George Mari george_mythusers at mari1938.org
Fri Dec 19 15:07:11 UTC 2008

Jake Anderson wrote:


> For me its a few personal experiences.
> I have a raid 0 setup (started before storage groups were available) and 
> if I watch something whilst something else is being recorded and 
> commflagged the little blue light is almost solid on. I had to add more 
> ram to the machine to let it record 2 shows and watch a 3rd. I needed to 
> go to 2gb of ram from 1gb, adding a further 2gb helped some more too.
> My fathers myth box which is a P4 3ghz (vs my Q6600) was doing about the 
> same job (without the commercial flagging, but as that is in realtime on 
> my machine it shouldn't affect disk IO much at all) will record 2 shows 
> and watch a 3rd with 512mb of ram and the disk light flashes at about 
> 1-2 Hz.

Well, to be fair, with RAID 0,5 or 6, (and probably 1), your drive light 
will be on more or at least as much as with a non-raid, single drive 
solution.  You're just spreading the same number of IO operations 
(slightly more with RAID5 or 6 because of the parity info) over multiple 
drives/spindles, so your system as a whole can do more IO.

If you have a 1GB system that is a combined BE/FE, that's probably a 
little tight on RAM, especially when comm flagging, mythfilldatabase and 
  possible transcode jobs run at the same time, so you may have been 
cutting into the swap space, and not necessarily hitting the IO limits 
of your RAID0.

I have a dedicated BE with 576MB RAM and an old SCSI card with 6x180GB 
drives in a software RAID5.  It's no trouble recording 2 shows, comm 
flagging them, and watching 3 other shows on my different FEs.  It sits 
in the basement, and is obviously not suitable for a living room or 
bedroom, but it's hardware I had lying around or was able to procure 


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