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SSD caching of spinning disks

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Antoine Durr
SSD caching of spinning disks
on Feb 13, 2013 at 9:04:33 pm

What kind of solutions exist to use an SSD raid to cache a larger spinning platters RAID? Is there anything that really does it seamlessly? Or even better, something along the lines of OS X's fusion drive?

http://www.anandtech.com/show/6679/a-month-with-apples-fusion-drive

Motivation: I'm looking to get more speed out of my RAID setup. I currently have a 16 drive array CI Designs SAS chassis controlled by an ATTO R680 in a Mac Pro. The setup works like a charm and has been very robust so far. But I need to go faster (currently in the 1300+ MB/sec range, aiming for 1800+ MB/sec). My goal is to reliably read 4K x 3K DPX files at 24fps. By the raw numbers, that's 48MB/frame * 24 = 1152, but from what I can tell, my Scratch system is "getting" maybe 60% of the raw read performance (and that discrepancy is also something I'm investigating).

That's where an SSD caching solution comes to mind. Rather than getting a bigger chassis with way more platters, I'd like to set up a small SSD RAID. However, I would like to avoid having to manually migrate files from a slow raid to a faster one. I'd like it to either be a true cache, or something like an OS X fusion drive (can it be done with ZFS?)

Any suggestions, beyond just getting a bigger chassis with more platters? Can I swap out a small handful of drives and replace them with SSDs and make 2 RAID volumes? But how then do I make the fast one act like a cache for the slower one?

Thanks in advance for any pointers or suggestions.

-- Antoine Durr


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Alex Gerulaitis
Re: SSD caching of spinning disks
on Feb 14, 2013 at 7:45:32 pm

[Antoine Durr] "What kind of solutions exist to use an SSD raid to cache a larger spinning platters RAID?"

Intel RST (Windows only), high-end NAS and SAN appliances; on a low end - some host adapters (Addonics AD2SAHSSD).

Don't believe there's anything mid-range for the Mac yet.

[Antoine Durr] "But I need to go faster (currently in the 1300+ MB/sec range, aiming for 1800+ MB/sec). My goal is to reliably read 4K x 3K DPX files at 24fps."

I'd rather investigate potential bottlenecks and improve the array's speed by using more/ faster drives, faster connectivity. Caching primarily works to improve response and IOPS numbers, not transfer rates of large files.

Alex Gerulaitis
Systems Engineer
DV411 - Los Angeles, CA


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Rainer Wirth
Re: SSD caching of spinning disks
on Feb 18, 2013 at 3:16:53 pm

It sounds to me, that your bottleneck will be the SAS.
For the speed you're looking for you need a 4way FC 8GB/s per lane with minimum of 16 drives plus the big FC Atto card.
Just replace drives won't do the job.
cheers

Rainer

factstory
Rainer Wirth
phone_0049-177-2156086
Mac pro 8core
Adobe,FCP,Avid
several raid systems


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Antoine Durr
Re: SSD caching of spinning disks
on Feb 18, 2013 at 6:58:52 pm

I know for sure that 16 spindles won't do the job. For dual 4k DPX streams I'll probably need 40+ spindles, and I'm trying to avoid having to add that many spindles. I'm wondering if there's an Apple like Fusion Drive solution, where you front-end the spindles with an SSD raid. I've seen some pretty huge read speeds on SSD raids, e.g. 3+GB/sec with a Highpoint card (yeah, I know, there's not a lot of love for Highpoint cards around these parts!).

My current direction is to just make a separate SSD RAID volume with the second card. 8 fast SSDs would most likely give me enough read speed. It's just that it's a separate volume, which is not an ideal setup, IMO. The workflow would be to copy needed data to the fast RAID, do color grading or whatever, and then replace it with the next batch of imagery.


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Alex Gerulaitis
Re: SSD caching of spinning disks
on Feb 18, 2013 at 7:44:01 pm

[Antoine Durr] "My current direction is to just make a separate SSD RAID volume with the second card. 8 fast SSDs would most likely give me enough read speed."

Sounds like a plan; would striping two PCIe SSD devices like Intel 910 series (up to 2GB/s read speeds each) work for you?

Alex Gerulaitis
Systems Engineer
DV411 - Los Angeles, CA


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Antoine Durr
Re: SSD caching of spinning disks
on Feb 27, 2013 at 8:18:04 am

It could, but those PCIe SSD's are insanely expensive (albeit the Intel's are cheaper than most). Reading one of the reviews on the Intel 910, it seems to present itself as 4 200GB drives, thus I'd have to do an OS based RAID 00 (stripe of a stripe?), raiding the 4 internal ones and then the two cards. That's 8 drives at RAID0, not my favorite combination!


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Fred Jodry
Re: SSD caching of spinning disks
on Feb 28, 2013 at 7:00:34 pm

You don`t have to be afraid of RAID 0 editing as long as you back- up and restore properly every now and then. Differently though, if you blow- up a live event take because your (usually the drives but occasionally something else) hardware fails, then that is a different matter. Remember that if you have to get running again quickly, then have labelled sets of spare drives and other hardware ready to swap in.


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Fred Jodry
Re: SSD caching of spinning disks
on Feb 28, 2013 at 7:03:14 pm

-For instance, sometimes a blown drive is really a drooping power supply, battery, or cable. Have one of those ready.


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Alex Gerulaitis
Re: SSD caching of spinning disks
on Feb 28, 2013 at 9:19:56 pm

[Antoine Durr] "That's 8 drives at RAID0, not my favorite combination!"

Most if not all high capacity SSDs are already RAID0 internally, just to put it in perspective. SSD failure rate is much lower than that of spinning disks. So RAID0 of a number of decent quality SSDs isn't as scary a proposition as that for spinning disks.

Alex Gerulaitis
Systems Engineer
DV411 - Los Angeles, CA


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