Okay, granted...this is a weird setup.  I have two internal SSDs for my cache array and 2 external SSDs in a USB3.0 caddy also in my cache array.  I ran out of internal ports... this has worked for the last year with no issues.  Today, I dismantled the server to add 2 fans, replace a Sata Cable (not due to a problem, just aesthetics), and clean out some very light dust.  I also took the time to do some cable management and route my CPU power around the back of the board rather than the front.  All connections checked and rechecked for mounting etc.  I plug everything back in and BOOM my cache is invalid.   My internal SSDs are showing up properly as sde and sdg. My USB3 devices are nowhere to be found on one of the USB3 jacks.  If I move it to the second USB3 jack they all show up, but now my external drives replace my internal drive letters with sdc and sdg on my external drives again invalidating my cache array.  I have double checked all connections and cables for issues and none can be found.   File system on the cache array is btfs and usually consists of the 4 discs.  Any way to save this??

Where are your USB3 jacks? On the motherboard shield or are they connected by a cable from the motherboard to someplace on the case? If the jacks are on the case, then it's time to check the cable. Is it firmly connected on both sides - and also check that you some sharp parts of the case hasn't damaged the cable. 

It's the top mount jacks. I am going to tear it all apart tomorrow and see if something is pinched or pulled some where. It all looks clean to me at the moment. But, I am tired and could be missing something.  I will report back either way so that folks have an answer.

Well, I have gone over the connects and nothing looks broken, bent, crimped, etc.  I never touched those wires also during the entire job.  I am baffled. And even though I have 1 port, it jumbles the drive letter assignments so I cannot get my cache back...along with my appdata, VMS stored there etc... ?

Drive letters may change when Linux is restarted.

unRAID recognizes drives by their serial number and should be able to rebuild the cache as before.

Can you post your diagnostics?

 

Good to know. Thanks!  I wish I knew what happened to my cace array then.

I wouldn't recommend using USB devices as cache or array devices, you're very likely to have issues sooner or later.

 

The diags might show something or you can use this FAQ entry to try and recover your pool data before re-formatting.

bonienl is correct.  I have seen Linux can start up consistently ordering USB ports (and network ports for that matter) 99% of the time, and then one day, it wakes up and decides to shuffle ports- for no discernible reason.  It can be maddening.  (Not actually speaking of Slackware- but I've experienced it in my work environment)

SSDs are now internal. It took some hair pulling (mostly re-cabling) but I got it done.  No more Cache drives on the outside.  Thanks everyone... Mistake made, lesson learned. Hopefully this will help others.