I’m moving my TrueNAS setup into a 15U wall-mounted rack with a hard 500mm external depth limit (450mm internal working depth). The problem is finding a single chassis that fits a motherboard, PSU, AND 6x 3.5" drives within that depth - they basically don’t exist at a reasonable price.
My solution is to split the server into two 2U chassis connected via external SAS:
Chassis 1 - NAS Server (400mm depth)
Supermicro X11SCH-LN4F-O
i3-8100 / 64GB ECC
Boot SSD on motherboard SATA
LSI 9207-8e HBA (external SAS)
Chassis 2 - JBOD Drive Enclosure (438mm depth)
6x WD Red Pro 4TB (existing RAIDZ2 pool)
SFF-8088 to SFF-8087 bracket adapter
2x Mini-SAS to 4x SATA breakout cables
ATX PSU with 24-pin jumper (powers drives only)
Connection is a single 0.5m SFF-8088 to SFF-8088 external SAS cable between the HBA and the bracket adapter in the JBOD.
My understanding is that I can install the HBA, connect everything up, boot TrueNAS, and simply import my existing pool since ZFS metadata lives on the drives. Boot drive stays on motherboard SATA throughout.
Am I missing anything obvious here? Anyone running a similar split setup?
I’ve been digging into this more and found a potential concern with my planned passive adapter approach. From this thread, the 1m SATA cable limit applies to the entire signal path, not individual cables. A passive SFF-8088 to SFF-8087 adapter doesn’t regenerate the signal.
My planned setup:
0.5m external SAS cable (HBA to JBOD)
Passive SFF-8088 to SFF-8087 bracket
~0.5m internal breakout cables to drives
Total: ~1m (right at the edge of SATA spec)
Given the chassis will be adjacent in the rack, I’m hoping the short run is fine. But should I consider adding a SAS expander (e.g. Intel RES2SV240) to the JBOD instead of a passive adapter? Seems overkill for 6 drives, but would eliminate cable length concerns entirely.
Has anyone run a similar DIY JBOD with passive adapter and short cables successfully?
I’d check the 2 rack chassis’ location for the 2 external SAS connectors. You might find a 250mm, (aka 0.25m), SAS cable for just this purpose. Unless you can’t get easy access to the rear to unplug when removing one of the chassis, a shorter cable should prevent the marginal length issue.
One note: In the past, I have found that average cables sustain the regular speed and reliability fine. However, better quality cables can have higher reliability when using for things like beyond spec distances. (Of course, some cheap cables can’t even support the normal max spec reliably, at reduced length!)
@NugentS - Good to have confirmation on the expander approach. Gives me confidence to proceed.
@Arwen - Great shout on the cable length. Both chassis are 2U and will be stacked directly on top of each other, so the rear ports will only be ~10-15cm apart. I’ll go with a 0.25m cable instead of 0.5m - cleaner install and should avoid any marginal signal issues as you mentioned.
Before I commit, are there any other gotchas I should be aware of? It feels like all I’m really doing is unplugging drives and reconnecting them via a different transport method - SAS expander instead of direct SATA. I’d imagine ZFS is pretty tolerant of that since it identifies drives by serial number rather than connection path, but wanted to check:
Should I export the pool first, or is it safe to just power down and reconnect?
Any issues with SMART data passthrough via the expander?
Will drive ordering look different in the TrueNAS UI afterwards?
Remember you will also need a way to spoof the PSU in the JBOD into starting up. So not just the switch on the PSU. Most PSU’s will not switch on without some indication of a load on certain pins .
As an aside, a generation or two later and the HBA will consumer maybe 1/2 the power of the 92xx series. The art of the server did some LSI HBA testing online (see YouTube) and it’s like 24w at idle for a 92xx series dropping down to 6W at a 9500 series. Even the 9400 series is like 8w.
@etorix - Thanks, good point on the lane count. I’ve got 2x SFF-8087 to 4x SATA breakout cables planned, which should give me 8 connections for the 6 drives. The Intel RES2SV240 expander will handle the fan-out from the single external SAS link. Does that sound right, or am I missing something?
Your expander has 6 ports, but they are all internal
I used an Adaptec (AEC-82885T) with 2 external ports and 7 internal ports. £26.00 on Ebay. May be a better fit as you don’t need to bodge the cables then.
Ah good catch, I hadn’t clocked that the RES2SV240 only has internal ports. The Adaptec AEC-82885T looks like a much cleaner solution - external ports built-in, no bracket adapter needed, and 12Gbps vs 6Gbps. At £26 it’s actually cheaper than the Intel + bracket combo too.
Just checking - the 82885T uses SFF-8644 external connectors, and my LSI 9207-8e has SFF-8088. So I’d need a SFF-8644 to SFF-8088 cable rather than SFF-8088 to SFF-8088 - is that right?
And on the ZFS question - any gotchas with just unplugging drives and reconnecting via the expander? Should I export the pool first or just power down and swap?
Would TrueNAS scale care if some of the drives were connected through the onboard motherboard sata and some were connected via the expander route in a separate server?
The question is caused by the fact that I’m having to rethink the JBOD case due to supply issues.
Another alternative would be to create two pools, one in the jbod and once in the Truenas box but they only have space for a max of 4 drives in each chassis right now
