ISCSI performance on atom

[jschuricht]

I am considering trying Freenas as a replacement to hardware raid at home. Anyways what I am thinking of doing is replacing a 26x 2TB nearly full hardware based RAID6 array with larger disks. I need to replace my existing controllers and expanders so the thought is to just build some 8 core Supermicro atom systems with 32-64GB ECC RAM, 12x 6TB ZFS Z2, LSI IT enabled controller, ~100GB mirrored ZIL and 4 1Gb MPIO links to present the entire array to a single windows server. This would add some extra overhead in the multiple layers but should give me the least trouble of mirroring a native drive in windows.

The 2 big issues that I am running into from the threads I have read are the 80% usage limit for ISCSI with an even lower recommended limit and ISCSI performance over ZFS.

On the 80% limit, is it just a performance hit when going >80% usage or is there some other issue I haven't read about yet?

For the ISCSI ZFS combination, how bad does this hamper speeds? Most of what I read was on older versions of Freenas with 5400 or 5600 series Xeons so it doesn't quite apply.

 

[Ericloewe]

Actually, 80% is the general limit. For iSCSI, you'd want it closer to 50%.

Mostly, performance will tank. Maybe not immediately, but over time it will. It is a very noticeable drop and it starts around 50%.

As for local performance, I don't think there are any problems with the Avotons (FreeNAS Mini owners will probably have some deeper insight). Do note that the mythical 16GB UDIMMs are hard to find and priced like rare relics. I believe no such DIMMs were ever validated by Supermicro, either.

 

[jschuricht]

Thanks, that may kill this idea. I can't afford to give up 50% of the available space for bulk storage.

 

[cyberjock]

Honestly, your idea was killed in multiple ways. 12x6TB drives are likely going to need more than 64GB of RAM (which means you can't use the Atom you were wanting). You'll also very likely need to do mirrors instead of RAIDZ2, or at least try to do 2 vdevs instead of one. You may also need to invest in an L2ARC.

From what you've said it sounds like unprepared for the money that will need to be spent for the hardware you need.

On the flipside I will tell you that my rather crappy E5606 can easily do some pretty good speeds (500MB/sec+ over 10Gb) so it is doable with the "right" gear.

 

[jschuricht]

The idea is only killed for Freenas. The current storage system is a dual 3Ghz quad core 5400 Xeons that I have been running since 2009 with 56GB RAM. It's on 10Gb and either the 15k drive arrays or the 7.2k arrays with the now old 8888ELP controllers have no trouble keeping up. I just don't see the point in wasting so much drive space. There is currently about 45TB of bulk data. Z2 with 12 6TB drives would be 30TB usable limited to 50% which would mean right off the bat I would need two $1600 atom nodes and $7200 of drives. I could buy 48 2TB drives for $3300 and have 80TB with 4x 12 RAID6 arrays. The question is why spend 2x for drives for 75% of the space? This is just a case of Freenas not being the "right" gear for this particular usage especially when you consider I am the only user and this is just a hobby with a $1500 electric bill that I would really like to bring down. :)