Preventing h/w RAID cards from dropping slow JBOD disks

Kevin asked:

I’m considering buying a used SAS h/w RAID card for externally attaching HDDs to an HP ProLiant I’m setting up.

However, I only require RAID functionality on some of the drives. Theoretically it should be simple to JBOD the other drives, but some of them are inexpensive SATA disks and probably cannot have TLER disabled.

I’d like to know, prior to actually ordering a RAID card, whether typically RAID cards would still enforce dropping of disks that do not respond within a few seconds, even if the disk is in a JBOD, and whether there is any way to disable this.

Ideally it would be nice to be able to select certain SAS ports that will be pass-through, bypassing the RAID engine entirely and just acting as an HBA for those ports. I know I could buy a separate SAS HBA but that seems like a waste of $ and is also impractical as it’s a 1U server so space is extremely limited.

My question then is whether the functionality I’m looking for (pass-through on certain ports or at least JBOD drives not getting themselves dropped due to slow response) is typical of proper h/w RAID cards such as PERC 5/E etc. I’ve browsed through the latter’s manual but unfortunately, as with most user manuals, it states the obvious and doesn’t state the unobvious.

Thanks for any info,

My answer:

The PERC series of RAID cards do not directly support JBOD, but it can be simulated by setting up each drive as a RAID 0 containing only one drive.

View the full question and answer on Server Fault.

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