LVM + RAID follow up

[blu at vl.com (Tom Metro)]

Derek Atkins wrote:
> My plan was to use this space for MythTV Backend Storage...

Likewise.


> SATA is only barely more pricey than PATA.

And in many cases there is no price difference.


> With 300G-400G drives (which is getting close to the minimum $/GB
> curve)...

A couple of months ago in preparation for building this MythTV box I 
analyzed the cost/GB of drives ranging from 250 GB to 750 GB, and as 
usual there was a premium to be paid for the larger sizes, and 250 GB 
was the lowest cost (26 cents/GB at the time), but 320 GB drives were 
very close (31 cents/GB), and noticeably lower than the 400 GB+ drives 
(40+ cents/GB), so I considered them the sweet spot. Of course prices 
are always dropping and now 400 GB drives are obtainable for under 30 
cents/GB.


> You can get a PCI SATA driver with... 4 SATA ports?

I picked up a Rosewill RC-209 4-port SATA card with RAID 0, 1 for about 
$30. There are plenty of options to choose from and this one seemed to 
have good reviews from Linux users. My choices were a little more 
limited due to needing a PCI card for an older motherboard. Most 
controller cards have moved to PCI Express.


> I use RAID-1 on all my servers now.
> I don't use LVM on those servers; It seems to add complexity...

RAID-1 is a no brainer, but what I wonder about is the use of higher 
order RAID or LVM layered on top of non-RAID volumes in the case of 
"budget" systems where you don't have backups (or at least frequent 
backups).

It's been raised on this list before, and from that and other sources, 
my understanding is that LVM can make data recovery a lot more difficult 
if one of the underlying drives fails. This is probably why LVM is 
typically layered on top of RAID sets.

In a more enterprise environment, recovery isn't really an issue. You 
create frequent backups (or continuous mirrors) and test them. But for a 
home MythTV Backend, I can see scenarios where you might chain a couple 
of large drives via LVM and no RAID to go for maximum space, and risk 
not having backups, yet would much rather be able to recover the 
surviving data from the LVM group if a drive fails.

  -Tom

-- 
Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
Professional Profile: http://tmetro.venturelogic.com/

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