[NTLUG:Discuss] Using SATA Drives to Replace Tape

[Pat Regan]

Richard Geoffrion wrote:
> Replacing tape backup with SATA drives.. Sure.. I do it and it works 
> DIRVISHLY.   I don't know about MAID though.  I don't personally know 
> any organization that needs that much backup storage.
> 

I am rarely comfortable with the idea of relying entirely on backups to
hard disk.  I am very comfortable with using online backups for daily,
and possibly weekly backups.  I am not very comfortable with it for long
term archival.

> I like the spin-down technology though.  I can see how it can save 
> money.  Spinning = electricity + heat.  Heat = Electricity to cool.   I 
> am curious as to how they do spin up.  They HAVE to stagger the spin 
> ups... Can you imagine the power supply that would be needed to prevent 
> brownouts if all the drives came on at once!!!

More importantly, less spinning == less drive failure...  Assuming they
are actually off for long enough periods of time between cycles.  This
article reminds me of a comment I read on Slashdot late last year.
Since it was just a comment on Slashdot I cannot confirm that this works
well in practice, but it sounds good in theory.

The guy claimed to have a rack full of machines packed with SATA drives.
 Each server was a single RAID 5 array.  Each server exported its RAID 5
array as a network block device.  Another server in the rack was used to
build a RAID 5 on top of the network block devices.

I don't know the exact details of his setup but at any given moment he
can lose one drive in each server, or he can lose any one complete
server, without any data loss.  I imagine if he loses the front end
server he would lose connectivity.  :p

When I read about this I did some quick shopping and some math.  You
could probably roll your own 4u servers with 16 500 GB SATA drives and a
pair of 3ware cards for under $10,000 (I forget the exact number I came
up with).  That gives a density of 8 TB per server.  More
conservatively, 6 TB with 2 RAID 5 arrays with hot spares per server.

One rack could hold about 10 of these, plus 2 1u front end servers.
That would give a total of 80 raw TB per rack at about $100,000 per
rack.  With RAID 5 over RAID 5 that would drop to 54 rather sturdy TB
per rack.

I would imagine using hdparm to spin down the drives would do a pretty
good job keeping most of the disks from spinning if you can be smarter
about the layout (no RAID 5 over RAID 5 I suppose).

I am not advocating this idea.  It seems reasonable though.  Anybody
ever try anything even remotely similar?

Pat