MythTV storage

[dsr at tao.merseine.nu (dsr at tao.merseine.nu)]

On Sun, Dec 24, 2006 at 08:25:21PM -0500, Robert La Ferla wrote:
> On a related note, I just picked up a couple of 500GB SATA drives for  
> a audio/video jukebox server.  What RAID configuration would you  
> use?  If I were to buy a 3rd drive, what RAID configuration would you  
> use?

For a pair of identical drives, your choices are:

0 Stripe -- write data across both drives simultaneously. Write
performance is improved. Read performance is normal. Capacity is
100% of the total drive space. Chance of volume failure is 200% of one
drive.

1 Mirror -- write the same data redundantly to both drives.
Write performance is normal. Read performance is improved.
Capacity is 50% of the total. Chance of volume failure is the
square root of one drive failure rate, plus the chance of
external causes. (It doesn't defend against both drives being
smashed by a big rock, for instance.)

Extension -- both drives appear to be in the same volume, but
the first 500GB is written to drive 1, then the second 500GB is
written to drive 2. No advantages or disadvantages over separate
drives unless the filesystem has problems when one drive fails.


When you add a third identical drive, you can also do:

5 Stripe & ECC: write across all three drives, adding a third
block of error correction. Write performance is slightly
improved, modulo the ECC generation. Read performance is
slightly improved. Capacity is n-1 (2, in this case) of total
drive space. Chance of volume failure is 1/3 of one drive, plus
the external cause chance.


For a jukebox server, you probably don't care much about data
storage reliability, but you also don't care much about
performance boosts or continuity of storage space. After all,
even largish video files are unlikely to be more than 10 GB or
so, and much more likely to be sub-1 GB. I wouldn't use RAID
here at all.

-dsr-

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