Cheap Port Multipliers - what not to do.

[Jens Bauer]

I've had a cheap JMB321 port multiplier on my EspressoBIN for more than a year.

I've used it with a BTRFS RAID0 configuration on two 1TB harddisks. This worked fine so far.

The day before yesterday I added another 1TB drive.

I added the first partition and balanced it. No problems.

Next partition, same thing, no problems (this was my web-partition with all my web-sites. Balanced fine).

Next partition was almost unused, added it and balanced it and ... segmentation fault.

This is not the fault of BTRFS!

No commands were available, I had no rootfs anymore.

I rebooted the board, nothing.

Started from SD, couldn't see anything but the SD-card.

As it's unlikely the 5 harddisks that were all fried at the same time, I decided to switch out the Port Multiplier (always have a couple of spare ones in the drawer).

Now I could see the drives again. Thus what happened was that when BTRFS started the balancing, the JMB321 overheated, because those cheap boards do not come with a heatsink. I did attach a heatsink to the spare one I had, so it'll postpone the problem for a while.

Unfortunately the web and mail partitions were both destroyed (those were the ones I balanced).

The other partitions are all intact and working.

 

-So I do not recommend using those cheap Port Multipliers, but if you do, please do yourself a favour and add a heatsink or keep the PM-board in the fridge.

Update: And never, ever use those cheap chinese SATA-cables that comes with the Port Multiplier - buy some that have a well-known quality brand on it. Also remember that SATA cables have a maximum mating count of 50 cycles (and no, they do not produce more SATA cables).

 

And remember: Real men don't make backups. ...

 

...They cry.