A question about external SAS ports.

natermeister

Limp Gawd
Joined
Dec 26, 2005
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463
Ok, let's say I build a 2U server that has a SAS/SATA RAID HBA and a couple years down the road, I need more space and don't want to build another server.

Is it possible to buy a rackable disc enclosure that can be added into the current array? I've seen the enclosures for such a setup, I've seen HBAs with external ports. But from a quick look around, all the RAID disc chassis seem to have a single SFF 8470 and the HBAs usually have an SFF 8088 connector(s).

Could anyone lend me some insight on this? I'd guess that they make 8470 to 8088 cables, right?

Thanks.
 
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Correct. We did just this with an LSI 3442E-R card, a 8088 to 8470 cable, a CBL-0167L assembly, a Supermicro 846e1 case, and a CSE-PTJBOD-CB1 power control board. It gives 24 drive bays for about $1600 including the controller. It's working very nicely, and I'd recommend it in a heartbeat.

We had to design our own hardware and software to monitor the power supplies of the JBOD, but this was easy and I can post schematics and source if you're interested.
 
See, the thing is I don't want the disc enclosure to be a JBOD...I want it to be part of the the RAID array in the main server. Still possible?
 
Sure. All that means is you'll want a RAID controller instead of an HBA. Something like the LSI 8888elp would work fine.

However, I wouldn't recommend making a single RAID array that spanned two enclosures, because really wide RAID stripes aren't possible (IIRC the LSI only supports a 32-disk-wide stripe), and if for some reason you need to boot the machine without the external storage connected you won't be able to access the array. Also, performance can go down when rebuilding the array on really wide stripes, and the chance of a disk failure goes up with a wider stripe, so that could cause a major problem.
 
Cool, that's what I thought, I just wasn't sure. Thanks for the help. I wonder how long it would take doing OCE with a extra 12TB or so...
 
running RAID60 on an 8888elp might be an option. You lose a few more drives in parity, but gain faster rebuilds (only the drives involved in the RAID6 subsets need rebuilding) and reliability (each RAID6 subset can survive 2 disk failures).

Any of th disks in the array can be on either the internal or external ports, and any disk can be accessed through a suitable expander if necessary.
 
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