[tech] Dead disk in Molmol

David Adam zanchey at ucc.gu.uwa.edu.au
Sat Mar 2 21:27:24 AWST 2019


Hi all,

Molmol has dropped one of its SSDs:

Feb 26 14:15:10 molmol kernel: ahcich1: Timeout on slot 25 port 0
Feb 26 14:15:10 molmol kernel: ahcich1: is 00000000 cs 02000000 ss 00000000 rs 02000000 tfd c0 serr 00000000 cmd 0004d917
Feb 26 14:15:10 molmol kernel: (ada1:ahcich1:0:0:0): FLUSHCACHE48. ACB: ea 00 00 00 00 40 00 00 00 00 00 00
Feb 26 14:30:34 molmol kernel: (ada1:ahcich1:0:0:0): CAM status: Command timeout
Feb 26 14:30:34 molmol kernel: (ada1:ahcich1:0:0:0): Retrying command
Feb 26 14:30:34 molmol kernel: ahcich1: AHCI reset: device not ready after 31000ms (tfd = 00000080)
(etc.)

It's detached from the bus and won't reattach.

The device is a Samsung SSD 840 PRO Series DXM05B0Q (s/n S1ATNSAD864731A) 
- note that there are two of these in the machine! I'm not sure whether it 
is hotpluggable or not.

This SSD was providing one half of the SLOG mirror [1] and a RAID 
partition for the root filesystem. The other half is provided by the 
other Samsung 840 PRO:

zfs pool status:

	NAME                             STATE     READ WRITE CKSUM
	logs
	  mirror-4                       DEGRADED     0     0     0
	    5535644740799039914          REMOVED      0     0     0  was /dev/gpt/molmol-slog
	    gpt/molmol-slog0             ONLINE       0     0     0


Checking status of gmirror(8) devices:
           Name    Status  Components
mirror/gmirror0  DEGRADED  ada0p2 (ACTIVE)

If one has gone, I suspect the other is not far behind (SLOG devices do a 
lot of writing), so it is probably worth replacing at least one and 
possibly both.

This may be part of why performance has tanked recently (although I have 
no evidence to support this statement).

They don't need to be big - we're currently using 80 GB of the 256 GB disk 
- but they do need to be reliable and fast. I have zero idea what the best 
part to pick is; any thoughts?

David Adam
zanchey@
UCC Wheel Member

[1]: 
https://pthree.org/2012/12/06/zfs-administration-part-iii-the-zfs-intent-log/



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