Sunday, November 23, 2014

Samsung SSD 840 EVO has a slow read bug: information on the fix

Over a year ago I switched my 2009 iMac from yet another dead hard drive to a Samsung EVO 840 1TB SSD. It was a calculated gamble that has worked fairly well so far, but SSD technology has proved less mature that I’d thought (Maybe this is why Apple has been slow to transition). For example, the net is full of contradictory recommendations on TRIM use. For another, the Anandtech coverage of this complex bug ends with “None of the big SSD manufacturers have been able to avoid widespread bugs”

Recently Samsung admitted they had a problem with slow reads — something I’ve been wondering about. They’ve put out  Windows fix and a bootable DOS version that’s supposed to work on a Mac.

I haven’t tried it yet, but I’ve assembled my references…

Thanks to Conrad’s Chavez’s generous blog post I feel ready to do this - once again I appreciate the CD drive in my old iMac. After BOTH of my backup systems are completely current of course. Actually, maybe I’ll do a 3rd back up just in case.

Update 11/25/14

Wow. I did the fix and the speed improvement of my 1.5 yo SSD is amazing. I’d noticed some operations were slow, but the gradual decline hid how bad things were. Startup time is maybe 2-10% of what it was.

I think extremely slow reads on something related to directory structure were causing my Time Machine/Time Capsule restore failures (more on that in the post, later).

A few notes/extensions of Conrad’s fine post:

  • I did 2 backups beforehand and tested a file restore from one. Then I did an additional Aperture specific backup to another drive.
  • I recommend booting into and running Disk Utility disk repair prior to the fix — just as a general safety measure.
  • Unplug all peripherals — keep it simple.
  • I didn’t have to rename the .ISO file to .DMG as Conrad mentioned. Disk Utility burned CD normally.
  • On my Bluetooth keyboard I hold down the ‘c’ key immediately after startup tone to boot off CD
  • Firmware fix is very quick — but the full repair took about 4.5h. The UI writes a dot every 15min or so (see below).
  • After the fix was done I got the old (I remember DOS) prompt. I pressed restart and got a heart attack as OS X was stuck in an exotic failed boot cycle. I had to press and hold power for a few seconds to force a proper shutdown. After that all was fine.

IMG 5216

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