All SSD build sanity check

[Redlined]

Hi everyone,
Over the last couple of weeks I've been looking at building an all SSD ZFS array form my home lab. First some background, in my day to day job I work with very large enterprise customers helping define and plan their virtualization strategies. This requires me to have a lab here at my home office where I can create environments to test ideas or try and recreate issues. Currently I have a ZFS datastore that I've been slowly tweaking, tuning, and upgrading as needed to meet my growing IOPS requirements, but at this point I want to stop the madness and start from scratch with a second array.

My goals are pretty simple, but I wanted to get some additional opinions for the experts:

• Approximately 500GB of physical storage
• DeDup for the pool - Almost all my machines are deployed from templates so this should increase my storage density
• Keep the other array as a Bronze teir of storage (home file server doesn't need to live on SSD array)

Based on my research it looks like the DDT would need approximately 20GB of space. In an effort to control costs (this build comes out of my pocket) I would look at a building a single socket multi-core box with 32GB of RAM. I know that I would have to tweak the Metadata setting to allow the full DDT table to be stored in RAM, but I think that is a fair trade off as the pool itself would be same speed as a L2ARC.

Currently I'm looking at either Intel 3500's or Samsung 840 Pro's, but would entertain others that others think would hold up. I haven't decided on size yet, but 3 x 256GB in RAID-Z should be enough. I could build two mirrors if folks think that would be a better route, but most of my reading that indicates that mirrors are only good for spinning disks.

Having a separate ZIL device(s) is still a question in my mind. I know that it would help protect the SSD pool from small writes without DeDup, but I haven't found any documentation that helps me understand if it would offer me any wear protection with DeDup turned on (since DeDup is in line or at least that is how I understand it).

Thanks in advance for any advice or suggestions !

 

[gea]

With SSDs you do not need mirrors, Raid-Z (1-3) is ok because they offer a much better I/O performance. Because of the missing trim support on raid and copy on write you should try to stay below 80% fillrate (below 50% if you really need max performance). Newest SSDs like Intel S3700 or SLC based ones can help but they are very expensive. But all newer SSD's are better than spindles.

I would avoid realtime dedup as it has two problems. If your dedup-table is larger than your ram, performance can be really worse (really worse means a delete snap command can last days). Even if the table fits into your ram, you would use this ram better for ARC, the read cache that gives performance. I would try to use lz4 compress and buy another ssd for capacity.

For home/lab use, I would avoid the ZIL and set sync to disable. This includes the danger of a 5s lost of last writes on a power failure. Do backups and optionally use a UPS. If you decide to use a ZIL with sync writes, you nead a really good SSD like a modern SLC disk or a Intel S3700 and even then its not as fast than without sync writes where a ZIL is not used/needed.

I would skip the ZIL and use a larger pool with a lower fillrate.

 

[Redlined]

Thanks for the information gea, I'll look at buying the extra SSD and skipping the De-Dup.