I can't find documentation to help me understand SAS RAIDS and Channel 1 versus 2.

Working from an existing example, using an ATTO R680 and a JBOD of 8 SAS hard drives I created a RAID 0 on Channel 1 that consisted of all 8 drives and on Channel 2 that consisted of all the same 8 drives. I now have sdc and sdd drives that I am able to mount and access.

I read that SAS drives have redundant paths, but how does channel 1 and 2 translate to sdc and sdd in SAS world?

Hi,

it's simply two connections (Channel 1 and 2) between the controller and the discs.

Most likely You will want to run a raid level greater than 0 (eg. raid-5) so You have redundancy just in case any of the discs will fail.

I suspect Your controller (ATTO R680, I didn't check the specs) can handle multipathing, too, so that Linux would only have one device (sdc and no sdd) to manage while the controller would handle I/O through multiple paths to the discs. That way, the controller would have the doubled bandwidth of two channels.

Anyways, as You have it configured, You might want to run a MD "multipath" device on top of sdc and sdd instead of a raid level, see kernel-sources/Documentation/md.txt for further reading and hints.

Take care that You don't use sdc and sdd as separate devices (i.e. mounting them...) as this will lead to data corruption. Either use sdc (exclusive-)or use sdd, not both at the same time.

Have fun!
Kind regards,
mdbuerkle

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Thank you this was very helpful. I was just confused by the fact that the OS would let me partition, format, mount, and write to both sdc and sdd as if they were separate RAIDs. I was starting think there was some sort of magic going on that turned my 2TB into 4TB.