[mythtv-users] Why RAID 5 stops working in 2009

[Another Sillyname]

2008/10/23 Mache Creeger <mache at creeger.com>:
> From Slashdot
>
> Lally Singh recommends a ZDNet piece predicting the imminent demise of RAID
> 5, noting that increasing storage and non-decreasing probability of disk
> failure will collide in a year or so. This reader adds, "Apparently, RAID 6
> isn't far behind. I'll keep the ZFS plug short. Go ZFS. There, that was it."
>
> http://blogs.zdnet.com/storage/?p=162
>
> -- Mache
>
> "Disk drive capacities double every 18-24 months. We have 1 TB drives now,
> and in 2009 we'll have 2 TB drives. With a 7-drive RAID 5 disk failure,
> you'll have 6 remaining 2 TB drives. As the RAID controller is busily
> reading through those 6 disks to reconstruct the data from the failed drive,
> it is almost certain it will see an [unrecoverable read error]. So the read
> fails ... The message 'we can't read this RAID volume' travels up the chain
> of command until an error message is presented on the screen. 12 TB of your
> carefully protected — you thought! — data is gone. Oh, you didn't back it up
> to tape? Bummer!"
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>

Given the amount of time it would take even a hardware controller to
reconstruct a 2TB drive you'd be unwise to use them.

750GB drives using a decent hardware controller take about 30 hours to
reconstruct a failed drive under raid 6.....this means you have a
'failure window' of those 30 hours when a 2nd failure kills you.  I
can't imagine I'd even want this 'failure window' to be in the 72+
hour timeframe.

I'd rather recommend using 2 x 8 port array controllers (with 750GB HD
under Raid6 and a hot spare)....so about 4tb usable and then mirror it
in real time to the 2nd array.......even with HD at 8GB an hour
(before compression) that's a lot of hours of programming before you
fill 4tb.