[mythtv-users] Questions about RAID

Andrew Davis andrew at nccomp.com
Fri Sep 29 17:33:07 UTC 2006

And keep in mind that RAID6 is quickly becoming a standard when dealing 
with SATA and IDE drives that have a higher failure rate. I'm not sure 
where support for it stands in Linux, but a RAID6 +1 HS is much safer 
than a RAID5 + 1HS. In a nutshell, in a RAID5, there's a task done 
called pre-fetching... also called disk scrubbing where it reads ahead 
and checks the writability of the drives. If a bad sector is found, its 
skipped. The problem is that if a drive fails, while a rebuild is 
occuring to a hotspare, disk scrubbing cannot occur. Thus, if writing 
data during a rebuild and a bad sector is found, the drive will be 
marked as failed and your rebuild will fail. This is why most h/w based 
SATA and IDE RAID controllers offer an option to "force a drive 
online"... though data corruption usually occurs. The solution is to 
either *always* do your array rebuilds outside the OS (only possible 
with a h/w controller, or in single-user mode if using a linux s/w RAID) 
or to implement a RAID6 solution.

Keep in mind that h/w controllers can speed things up a bit too... but 
you'll want to check the kernel docs for supported ones.


Steven Adeff wrote:
> On 9/29/06, OJ <ole at legaard.net> wrote:
>> Hi
>> I have started to move my music, pictures, and movies to my MythTV
>> backend server. My backend server is a AMD64 server with 1 250GB HD and
>> 512 MB RAM.
>> 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?
> if normal backup is not a realistic option then yes, RAID is the way
> to go, in your case, I'd suggest RAID5.
>> 2. Is it possible to expand this RAID array later (insert an extra HD)?
> with RAID5, yes. its a relatively slow process but it works.
>> 3. My DVD collection will use a lot of HD space. Any suggestions on how
>> to reduce the file size (divX, ...)?
> or x264, which is gaining in popularity amongst those with the CPU
> power to decode it. For DVD conversions this isn't all that much
> horsepower in all honesty and the quality difference is outstanding,
> you'll basically get minimal quality loss at a great reduction in
> size.
> Sadly, the best software for the conversions is for windows (mplayer
> can do it, but from what I understand, is not all that ideal for it),
> the good news side of that is from what I can tell, the software will
> all operate under WINE.

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