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Kevin
Asked: 2013-01-22 21:23:02 +0800 CST

Can IBM System x3650 passthrough SAS?

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I am looking at the specs and manual for the IBM System x3650. According to the specs a ServeRAID-8k-l hardware RAID comes standard, but there's an option to upgrade to ServeRAID-8k. If I understand this correctly, this system will always have some h/w RAID.

I have found that h/w RAID firmware often assumes that all disks attached should be part of a RAID configuration managed by h/w, and of the same make of h/w at that. This won't always be the case, either because one is using s/w RAID and/or because HDDs are being brought in from other systems with data on them.

My question is whether this limitation applies to the x3650 or whether the on-board SAS ports can 'pass-through,' allowing the OS to 'see' an attached physical disk directly.

(I'm quite cautious because I once bought an Adaptec RAID whose specs and manual claimed it had this capacity, only to find out it didn't.)

I'm also wondering of the same on-board controller, notwithstanding the usual cautions on using disks that big, whether it is able to talk to 2TB disks (I've seen some that don't).

sas

2 Answers

  1. Best Answer

    Both of the RAID cards (8k or 8k-l) you are considering are able to configure the drive as a "Simple Volume". This is done in the ServeRaid Manager management software bundled with the server. documentation here

    This simply exposes the drive as a single LUN. This approach is often used when recovering damaged RAID arrays for example. (However, see the comments below.)

    It seems that these controllers however have only been updated to provide support for 2TB drives. There is no mention of 3TB device support in the most recent firmware update.

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  2. If you want to do this the right way, you'll need a standalone SAS HBA.

    See: ZFS SAS/SATA controller recommendations

    However, sometimes, I will configure ZFS on top of hardware RAID arrays. This is typically when I'm looking for ZFS filesystem flexibility or specific features (like compression). Also, if you have a high-end RAID controller (like an HP Smart Array), leveraging its battery or flash-backed cache is more convenient and affordable than a proper ZIL device (STEC ZeusRAM or DDRDrive) and still gives you the low-latency write speed.

    Remember, without either of the above options, you won't have a real write cache...

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