SSD ARC Drive?

[cmdematos]

Should I or should I not add a 120Gb SSD for the ARC/LOG drive?

I have the following hardware ...

4x 500Gb 7200rpm JBOD on Dell Perc5i raid card set to non-raid (RAIDZ1)
4x 1gB 7200rpm JBOD on Dell Perc5i raid card set to non-raid (RAIDZ1)
4x 2Gb 7200rpm JBOD on Dell Perc5i raid card set to non-raid (RAIDZ2)

2.8Ghz Intell X5560 6Gb Cache
24Gb Ram

The SSD would be some inexpensive 120Gb or 250Gb Drive, probably a Samsung 840 EVO.

The Dell PERC 5 raid cards where once employed in RAID10 and each has 512Mb RAM. They now do duty on JBOD mode and ZFS handles the RAID.

Do I gain much (anything) by adding the SSD? Is it advisable?

 

[willnx]

You're likely hood of seeing any performance gains by adding an inexpensive SSD are slim at best.
It's more likely that you'll see a loss in performance by adding the SSD.

The one exception here is if you're using the NAS as an NFS datastore for a pile of VMDKs, then setting up the SLOG *might* provide a performance gain.

SSDs are faster than HDDs, but RAM is still leagues ahead of either.

Side Note:
Those Dell Perc 5i cards; when you say "JBOD mode" do you mean you've flashed them to IT mode, and they're running as an HBA?

 

[cmdematos]

WRT:
'Those Dell Perc 5i cards; when you say "JBOD mode" do you mean you've flashed them to IT mode, and they're running as an HBA?'

I mean I created 4x volumes of raid 0 with one drive in each, and pulled the battery for good measure to disable writeback. They are functioning as standard SATA controllers with some readonly cache on them, no raid code should be running on them in this mode, they are just serving up blocks.

I do not expect them to be faster than the SATA2 controllers on board the T5500 Dell Precision board, but they are providing consistent access and the cabling was in place in any case.

 

[cyberjock]

Yeah, RAID-0s are NOT JBOD. You are doing nothing more than putting ZFS on RAID. You know, that terrible thing we keep telling people not to do, and they do anyway and lose their data.

If you search around the forum for Perc 5i info you'll find there is NO way to use a Perc 5i in a fashion that is reliable for ZFS, and you'll probably find a few people that have lost their pools to the bad assumption that single disk RAID-0s are safe. They aren't.

 

[jgreco]

Well, they're JBOD, they're just USELESS JBOD because what they mean is that the disks are individually addressable, but what we want is to be able to talk to the disks above and beyond that, and be able to access SMART and not have any RAID interference at all. We need HBA mode.

Some Dell controllers like the PERC H310 can be bludgeoned into 9211-8i mode, but the process is more difficult than an M1015 because you've got to take it through a firmware downgrade to an early Dell firmware, step across to an early LSI firmware, then you can update to P16 or whatever. Just finished losing a few hours doing this for someone recently so I'm still silently cursing.

RAID-0s

Yummm... hard drive flavored cereal

 

[Ericloewe]

Yummm... hard drive flavored cereal

Now with 15% less sugar and 20% more awkward typesetting!