SSD ZIL mirror

[vitek]

Thinking of getting 2 ssd in raid1 as a ZIL.

Would two of these http://www.corsair.com/en/ssd/nova-...30gb-solid-state-hard-drive-cssd-v30gb2a.html drives work good?

Or should i go for the Intel 311 20gb SLC but thats like double in price.

Would it be a big difference or what should i look for?

 

[louisk]

Unless you're pushing >1G/s, it won't do much of anything for you. You'd probably see more benefit in putting the SSD as an L2ARC.

If you're doing >1G/s, get a stec zeus ram (http://www.stec-inc.com/product/zeusram.php). 8G is plenty. ZIL isn't big.

 

[survive]

Hi vitek,

For the ZIL you really want SLC flash. It's more durable....since all the ZIL does is writes you can "wear out" an MLC SSD quickly.

Unless you are pushing a ton of writes or doing NFS with ESXi it might not really make much of a difference. What's the use case\problem you are looking to solve?

-Will

 

[Joshua Parker Ruehlig]

If your going 311 get the slightly updates 313, it has higher IOPS. Unless your getting the 311 at a much lower price

 

[vitek]

Thanks for all the answers. I am doing NFS with ESXi and its really slow. Have gone over to ISCSI temporarly because of this. Also there is also quite some small writes from time to time via bittorrent at high speeds. Ok ill check for prices for the 313.
You say the SSDs will wear out. How long are we talking about? And wouldnt it be preferable to get some extra GB if its not overly expensive to have more GB for wear leveling?

 

[Joshua Parker Ruehlig]

I researched this myself before and never found solid data to prove either point. Yes extra GB for wear leveling would help, but at the same time FreeBSD doesn't yet have trim in zfs so the OS may not even use those 'extra' blocks, it might just keep rewriting the same blocks over and over, so blocks that last longer matter, not having more blocks. I read somewhere the zil is rewritten every 5 seconds and having over 5 seconds of zil write space for your pool is not used.

There was a bunch of debate / arguments over on the HardForum but no one had data for wear, and block damage, likely because SSDs haven't been in practice long enough for any real study's to be done.

 

[markw78]

Even after you've used all the "fresh writes" on the SSD, the SSD is still pretty fast, instead of a "write" its a "delete - write" if I'm not mistaken, on a fast SSD thats still going to be faster than any spindle out there, right?

 

[cyberjock]

I just realized something. If you REALLY want a ZIL, something like the Acard ANS-9010 would work well. I have several of these in sizes of 8-32GB, but as a ZIL, they would rock!

Here's a link to one model: http://www.acard.com/english/fb01-specification-print.jsp?idno_no=382

 

[paleoN]

If you REALLY want a ZIL, something like the Acard ANS-9010 would work well. I have several of these in sizes of 8-32GB, but as a ZIL, they would rock!

This could be much better.

Supports unbuffer and non-registered ECC/Non-ECC DDR2 400/533/667/800 DIMM**
SATA 3.0Gbps Interface port

Gah, we want ECC RAM and it's DDR2 to boot. We also want 6Gbps SATA. The rate it for 20,000 IOPS, but fail to mention the IO size. Bandwidth wise it's only 200MB/sec. You would like throughput to be higher. Given that it's DRAM, it likely has very low latencies. Which is the, or at least one of the, most important aspects for a ZIL. I didn't check, but I imagine price is quite high as well.

Currently, I don't believe they make a decent DRAM based ZIL device. You would probably be hard pressed to find a decent flash based one that doesn't cost an arm & a leg as well.

 

[cyberjock]

The ANS-9010 series support ECC RAM. If you choose not to use ECC, then 1/9th of your space is lost as the box creates it's own parity. One of the ANS-9010s has 2 SATA ports and a jumper change turns the 1 physical drive into 2. Ideally, you can setup a RAID0 with the 2 "drives" and double the speed. I get something like 430MB/sec off of my dual port box with a software RAID0 on Windows 7 x64. I haven't benchmarked the single port drives in a long time, so I can't remember exactly what they get. I do know that a firmware update did increase the performance a while back.

When I bought my boxes the prices were $350-450(single and dual port), then you just have to buy DDR2 RAM. Unfortunately, the box doesn't support DDR3 since DDR3 was just starting to hit the market when this box was released. I think 4GB DDR2 sticks of RAM are like $60 or so each, but they shouldn't ever "wear out" since they are all RAM. A $25 battery will need to be replaced every so often (5 years? I've had all of mine for 4 years and had zero failures) to protect your data in case of a loss of power.

Have come up with questions now that I've thought more deeply about this whole thing. See http://forums.freenas.org/showthread.php?9424-Ramdisk-as-ZIL&p=40662#post40662 if you want to continue the conversation about the ANS-9010 series as I don't want to hijack the thread.