[s-cars] NAC- need advice on photo workstation, RAID and some other ???s

[Theodore Chen]

--- Taka Mizutani <t44tqtro at gmail.com> wrote:

> Teddy-
> I'm thinking of a 3-4 drive RAID 5 array, with EMC Retrospect software
> running
> my backup to external USB HDs, sequentially backed up weekly (I don't have a
> constant influx of data to require daily backups).

that'll work fine.  use 4 - it'll be significantly faster.

> The reason for the RAID array is also for future expandability- I do foresee
> hitting that 2Tb limit eventually.

wow, that's a big home data center.  there was a time when you had to buy
gigantic storage machines from IBM to store that kind of data.  now you can
get 2TB for $800 (4 x 500GB HDs at $200 each).

so you'll break it up into multiple LUNs, each with 2TB?  RAID would
definitely make this easier, though i believe there are other ways to deal
with the 2TB (not 2 Tb) limit in windows.

however, if you want to add more drives, i think you'll have to add
them as a group of 3 or 4 - same size as your initial group, configured
so that you effectively make each of the original drives bigger, and 
it won't have the performance of an 8 drive array.  otherwise, you have 
to rebuild the volume and recalculate all the parities.  it probably
depends on the features in your controller, but i don't think adding more
capacity to an existing RAID array is as simple as plugging in a new drive.

> If I have file corruption, my only saving grace would be the backup, that's
> correct. At least with hardware RAID as opposed to software RAID, the 
> chances of array corruption are much lower- software RAID sucks IMO.

from a reliability standpoint, i'd also prefer hardware.  software RAID
can be faster because it uses your GHz CPU rather than the onboard MHz CPU,
but it becomes subject to the whims of the OS.

it's not just file corruption.  there's probably not many people here who
haven't typed rm -rf * in the wrong directory or copied the backup onto 
the source.  backup lets you bring back stuff you accidentally deleted.

> Since I missed out on getting a couple more WD 320s at Best Buy on
> clearance, I'll get some more when I place my order for the SATA RAID 
> card.
> 
> One more thing- more directed not to you, Teddy, but to others:
> What are the consequences of mixing different capacity drives with a 
> RAID 5 or RAID 6 array?

you can do it, but the extra capacity of the larger drives will be wasted.
the RAID array will only store data until the smallest drive reaches
capacity.

RAID 6 is overkill, IMHO.  you're going to take two drives for parity
instead of just one as with RAID 5, and i don't think you're going to
get much additional protection over a RAID 5 with Retrospect backups.
RAID 6 guards against double disk failure, which is much less likely
when you have a relatively small number of disks.  if you were going to
run a 1000-disk farm, i could see using RAID 6, but you're talking about
single digit numbers of disks.  it's hugely inefficient unless you have 
a large number of disks.

> I've narrowed it down to the Promise 8350 and the Areca 1220, both 
> 8-port SATA RAID cards running a dedicated Intel RAID processor w/ 
> onboard cache (256MB IIRC) on a PCI-E bus (x4 on the Promise, x8 on 
> the Areca), both supposed to be blazing fast, esp. the Areca.

nice setup.  you can add 4 more disks later and set up a new LUN so you
don't have to worry about the 2TB limit.

FYI, i may try this winXP hack to unlock the RAID capability that normally
requires you to buy winXP server:
http://www.tomshardware.com/2004/11/19/using_windowsxp_to_make_raid_5_happen/index.html

-teddy


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