If you put 5 Seagate ST31500341AS drives, (which will max out @ 120 MB/sec) on a port-multiplier backplane, won't that oversubscribe the SATA II port connected to the backplane?

Lessee... Sata II provides 3 Gbits/sec = 3000 Mbits/sec divide by 8 for Bytes = 375 MBytes/sec

5 drives maxed out (120 MBytes/sec * 5) = 600 MBytes/sec

So for max port multiplier utilization you would only want 3 drives per SATA II port, for a max of 360 MB/sec, which will fit under your 375 MB/s SATA II port throughput.

Does a 1.5 TB Seagate AS series drive really deliver 120MB/sec sustained? Maybe you could get away with 4 drives per port-multiplier backplane, but 5?

I suppose if you paid attention to which spindles were attached to which RAID you could make sure that all 5 drives per backplane weren't reading or writing at the same time.

Wouldn't LVM have more flexibility in this regard than mdadm?

.../Tom

-----Original Message----- From: studiosysadmins-discuss-bounces@studiosysadmins.com [mailto:studiosysadmins-discuss-bounces@studiosysadmins.com] On Behalf Of Andrew Klaassen Sent: Wednesday, September 02, 2009 10:19 AM To: discuss@studiosysadmins.com Subject: Re: Question about network deleting.

--- On Tue, 9/1/09, Klaus Steden klaus-s@moving-picture.com wrote:

You could try one of these ...

http://blog.backblaze.com/2009/09/01/petabytes-on-a-budget-how-to-build- cheap-cloud-storage/

I've been thinking about building something like that, but I've had a hard time finding good info about port-multiplier backplanes. The good news is that Backblaze seems to have a working, well-tested config using port multipliers; the bad news is that they thank "James Lee at Chyang Fun Industries in Taiwan for customizing SATA boards to simplify our design". I probably don't have the buying power clout to get James Lee - as nice a guy as he might be - to do that for me. (Although... if they have a few extras left over from the Backblaze build...)

Andrew

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