Disk Shelf

[NickF]

Hello Everyone,
I'm looking for a disk shelf for my R710 for future expansion capabilities, and I am wondering what I should be looking for.
I guess I would like a 12bay 2U chassis if possible which would connect to my main box with a SAS 8088 connector or two...and would like a relatively cheap option <$400. In terms of noise it has to be relatively quiet, at least around the volume levels of the R710. Is the MD1200 a good option for FreeNAS? Are there any cheapish NetApp shelves? All I could find on eBay at low cost are 24 bay shelves and I think that would be a waste of electricity as I will definitely not be able to populate that many drives in the lifetime of this server.
Any suggestions?

 

[Arwen]

I don't have specific suggestions on products. But, you do need to understand a few details,
(in case you don't already).

SAS controllers, (like ones that use a 8088 type connector), can connect to more disks than
the number of host ports. Meaning if you have 4 host ports, they can connect to 12 disks in
an external chassis. BUT, you need something called a SAS Expander.

If you want cheap, then generally you have to avoid SAS expanders. This means more host
ports. So for a 2U 12 disk expansion chassis, you would need 12 host ports, (usually through
4 port connectors). End result, you would need 3, 4 port cables, and 3 host ports of 4.

SAS expanders add cost, but allow lots of disks per host port. They can be built into the disk
back plane, or be a separate item. They can have 16 ports or upto 36 ports. You use 4 or 8 for
the host side, and the rest for the disk side.

Don't under any circumstances buy a SAS 1 controller or expander. They have a 2TB disk size
limitation, (since the SAS 1 standard came out before larger disks).

 

[NickF]

Hi Arwen,
I was assuming that the device I want has 1, preferably 2 8088 connectors on the back (for additional speeds/IOPS) and a SAS expander.. because I would ideally like to connect it to an LSI 9207-8e or similar and just run the two SAS connectors, allowing me for the maximum throughput for scrubs and backups and stuff. I mean, I can really get away 8 drives if they make something that has two 4 to 4 backplanes.

It is not necessary to be rack mount, but it would be ideally. I could perhaps connect two external SATA IcyDock 4 bay things and power them with a PSU that is jumped to always be on? There appears to be breakout cables capable of doing this.
http://www.icydock.com/goods.php?id=154

ANy suggestions are welcome!

 

[Arwen]

You have to be careful with SATA devices. They have a more limited cable length. Thus, if you were to use 2 x SATA
IcyDock 4s, (for 8 disks), you need to keep the cables to SATA specifications. (Don't forget to add the external cable,
the internal cable and any connectors for resistance and capacitance.) The only way to get longer cables is with a SAS
controller WHEN used with either SAS disks, OR SAS expander.

Basically, a SAS host port turns into a SATA host port, (electrical and protocol), when connected to a SATA disk. With
cable length limitations.

When a SAS expander is in the mix, you get the full cable length of SAS, between the host port(s) and the SAS expander
chip. Then, any SATA disks connected to the SAS expander use the SATA electrical and protocol. The SATA protocol is
then tunneled through SAS to the host port(s).

Some what complicated.

However, using a standard PC chassis with standard PC power supply, (proper wattage for the number of disks), is potentially
a cheaper way to go to expand your disks. You can either use shorter cables with SATA protocol, or put in a SAS expander
in the expansion chassis. You have to decide if the risk of having some disks external and some internal is acceptable. If you
loose power to the external disks, generally your ZFS pool will be auto-exported. And in rare cases, the pool can be lost
completely.

SAS expanders can be found that have PCIe form factor. Some will take power either from a PCIe slot, or a 4 pin MOLEX
power connector. Thus, you can put them in a PC chassis that has no motherboard.

Anyway, this is not just for you. I wrote it down to train myself in thinking SAS. Plus, for anyone else reading this post.