07-30-2013 02:25 PM
Is there any way to put a p812 controller into JBOD mode? We want to use software RAID with a large number of disks. So far I haven't found a way to allow the OS to see indivudal drives that aren't part of a RAID volume on the p812.
07-30-2013 04:20 PM
Not in a ProLiant system (HP-UX is different).
Instead, you can create a set of RAID-0 logical drives each containing a single physical drive. Smart Array controller will still provide the non-volatile write cache to speed up writes, manage SMART warnings, control the drive LEDs, etc.
07-30-2013 08:44 PM
It's possible to use smartctl/smartd for on disks that are behind a smart array controller. But perhaps you're doing this for another reason? ZFS? Perhaps you want to try first if you get better performance with many RAID0 or if it's actually better with less arrays. It's certainly easier to manage with less arrays.
Another question I'd have: how many arrays can you create on a P812? I couldn't find it in the quickspecs, only that it maxed out at 108 disks. Can it also do 108 arrays and 108 logical drives?
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07-30-2013 09:47 PM
Thanks very much for the replies so far.
We have a few DL380 servers that connect to MDS600 disk systems via P812 controllers. We're aiming to manage the raid arrays using software raid (mdadm) to allow for specific options (RAID 10 far 2), ease of monitoring using standard linux tools, and survivability of hardware failure (as software raid should be able to be reassembled using different hardware if needed).
Setting up every drive as a RAID 0 volume is an option as long as there's no performance penalty (and Robert's post indicates that there would actually be benefits), but this would be cumbersome to manage considering that each MDS600 would hold 70 drives to be manually set up as individual RAID 0 volumes (multiplied by four server/disk system pairs).
Barring any new information we'll test performance on both hardware RAID 10 and software RAID 10 far 2 over hardware RAID 0 and evaluate from there. I just wanted to make sure we weren't missing an option to allow the OS pass-through access to drives not in a hardware raid volume.
07-31-2013 08:50 AM
That controller is limited to 64 logical drives, so won't quite support 1:1 mapping of an MDS600 filled with 70 drives.
Although it'd be awkward to manage a large number of logical drives with the ACU GUI, the command-line version shouldn't be too bad (invoke from a shell script or perl script).
07-31-2013 02:38 PM
Thanks Robert, that hpacucli tool was exactly what I was looking for. Writing a batch script to create RAID0 volumes for all unassigned drives on a controller was easy.
If anyone's interested, with an eight drive test we're not seeing any significant differences in read and write tests between software RAID10/hardware RAID0 and hardware RAID 1+0, although hdparm reports that the software/hardware hybrid has somewhat faster buffered disk reads.
The HP product info page on the p812  states that it supports up to 108 drives...hopefully that's the case, as that's why we purchased them.
10-15-2013 01:35 AM
For future reference - buying a p812 and using it for jbod is like using a ducati motorcycle for a generator. It is both wasteful and inefficient. For zfs etc you are going to get better performance and reliability using one of the recommended cards (LSI is common) that are designed to run in a straight through/hba type mode.