Pure SSD?

[MDMurdock]

A coworker and I were thinking about a homemade flash array, something like a Violin or Tintri to a lesser extent.

Is there any reason, besides cost, FreeNAS couldn't handle a bunch of pure SSD drives in RAIDZ1? Something like 8, 12 or more 512GB SSD drives? Could I expect a few hundred thousand IOPS? Over 500K?

Thanks!

 

[cyberjock]

I would expect amazing IOPS. But I'd definitely make sure you have a very powerful CPU if you have a need for high IOPS. Keep in mind your limiting component will be your network speeds, which you could easily max out with far bigger and less expensive drives.

 

[jgreco]

Also, "IOPS" in the context is not straightforward; you'll find your delivered IOPS are very much dependent on the NAS/SAN protocol in use, and dependent on the client as well.

which you could easily max out with far bigger and less expensive drives.

Well, now, that really depends on the workload, doesn't it? If you have ten spindles and each is capable of 5ms seeks, it should be obvious that each individual spindle cannot possibly seek to more than ~200 locations per second, so you're limited to a maximum possibility of 2000 random reads per second, quite possibly less depending on specifics. If you're doing 2000 random reads of 512 byte records, your spinning rust array will max out at 1MByte/sec. However, a SSD, not having the same heavily seek limited characteristics, that'll perform very well under such demand.

The TrueNAS guys use the Fusion-io stuff to drive their IOPS numbers, but the cost for Fusion-io ioDrive cards seems to be about 15-20x the equivalent cheap SSD. It'd be interesting to slap together a FreeNAS system with a quartet of SSD's to see how it works out. If I went and did this, what would the preferred test be for IOPS? NASPT? Anyone want to play?

 

[MDMurdock]

10Gb Ethernet or 8Gb Fibre (supported in FreeNAS?) would be a must with this many IOPS. What I'm interested in is; given good CPU and RAM and HBA IO, can FreeNAS handle this many IOPS?
Does it even care?

 

[jgreco]

You're confusing IOPS and bandwidth. 500,000 IOPS involving a 512 byte read is 256MB/sec, which is about two gigabits. 500,000 IOPS involving a 4096 byte read is 2048MB/sec, which is about seventeen gigabits. The bandwidth required is a function of the number of IOPS and the size of those transactions. However, in a NAS environment, it may even be more complicated, because a single NAS protocol request of a small size may drive the NAS engine to begin several IOPS, particularly something like file opening or creation.