raid - Adding nearline SAS disks to a controller with SAS disks

I have a Dell Poweredge 840 server that currently has a pair of hot swappable 146Gb SAS disks attached to a SAS 5IR controller, configured as RAID 1.

I have two spare slots to add two add more storage, and have a need to add a relatively large amount of storage as cheaply as possible. The data on the new disks will mostly be temporary file storage.

I've explored adding SATA storage to the on board SATA interface, which is limited to 1TB per SATA disk, and am now looking at alternatives. I'm wondering about adding nearline SAS drives to the existing controller to give me lots of storage at near SATA pricing.

I'm a little nervous about mixing SAS and nearline SAS disks on the same controller even though no volumes will ever span the two disks types. I'm looking for advise on whether this would be a good idea or not?

I'm considering adding either 1 or 2 disks with a capacity of 2TB each. If I add two disks, I'll likely configure them as RAID 0 as capacity is more important than fault tolerance.

Answer

SAS uses higher signalling voltages than SATA so mixing those on the same backplane isn't the best of ideas, although you can get SATA interposer cards to allow SATA to be used on the same backplane.

Near line SAS however uses a proper SAS interface so there should be no issue with your intended setup even if you put them all on the SAS 5iR.

I would suggest using the SAS 5iR rather than the onboard SATA for a few reasons - the 5iR will be connected to your hotswap backplane and the onboard SATA won't. Also from my experience the onboard SATA on most poweredge's is just a basic SATA controller that doesn't support RAID in any way shape or form.