[mythtv-users] Questions about RAID

Andrew Davis andrew at nccomp.com
Fri Sep 29 17:25:47 UTC 2006

I just built my first myth box last week and set it up this last week 
and previous weekend. I went with 3x250GB SATAII 16Mb cache drives in a 
s/w RAID5. Additionally, I bought a single 500GB SATAII drive for 
backups (note: these are for storage only... the actual OS, root 
filesystem, swap, etc are on a two-drive RAID1 of 2x120GB SATAII, 8Mb 
cache drives (though they're connected to SATAI ports on my mobo... my 
mobo has 4xSATAII and 4xSATAI ports). I setup the RAID5 to use just a 
little less than actual space available to ensure that the final 500GB 
volume would be smaller than the standalone 500Gb volume. The result is 
that its actually about 478GB of usable space while the standalone 500Gb 
drive is 482Gb usable. I then ran an rsync job to copy everything from 
the RAID5 to the standalone 500Gb drive. That job now runs at 2am 
nightly in cron and sync's over only the changes from the RAID5 to the 
500Gb drive... takes about 20 minutes to an hour depending on how much I 
recorded that day or how many new DVDs or CDs I've added to my 
collection. The end result is the peace of mind of the RAID and the 
extra measure of a backup. I also tried connecting the 500Gb drive via 
an external USB2 enclosure and updated the device path in my rsync 
script and it worked just fine. The enclosure supports USB2, Firewire 
400, and Firewire 800. When doing the same thing on the Firewire 800 
port, it was even faster. This is probably a safer backup means, but I 
have a one year running around the house, so its not practical right 
now. Perhaps in a few months I'll do a wireless USB solution? :)

Robin Hill wrote:
> On Fri Sep 29, 2006 at 10:35:03AM +0300, OJ wrote:
>> Now I'm starting to worry about all my data. The problem is that it is
>> starting to become a huge amount of data so normal backup is not an
>> realistic option for me.
>> I'm thinking of buying 3 250GB (or maybe 500GB) HD and setting them up
>> with software RAID.
>> Questions:
>> 1. Is RAID the only solution for this purpose?
> Pretty much, yes - you could backup to disk, but that's just a less
> efficient form of RAID mirroring.
>> 2. Is it possible to expand this RAID array later (insert an extra HD)?
> The latest Linux software RAID tools allow the expansion of an array,
> yes.
>> 3. My DVD collection will use a lot of HD space. Any suggestions on how
>> to reduce the file size (divX, ...)?
> More efficient codecs is the best way to go - MPEG4 (DivX or XviD) is
> probably your best bet at the moment, as h.264 doesn't seem very well
> supported yet.  These should allow you to re-encode at lower bitrates
> without any perceptible quality loss.
> Cheers,
>         Robin
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