Fooled by Western Digital

Today I read “Western Digital admits 2TB-6TB WD Red NAS drives use shingled magnetic recording” .

I am one of those who were fooled by Western Digital… A while ago I equipped a server with 2 units of the WD20EFAX hard drive in a software RAID1 array. Unfortunately, these are among the models falsely marketed as “not SMR” until WD was pressured to admit otherwise.

The problem with SMR (compared to PMR) is that data are written in overlapping “shingles”, each multiple megabytes large. Write/overwrite operations involve the firmware doing housekeeping to deal with the target shingles as well as these around them. Write performance thus suffers, especially in random writes, e.g. multiple users writing multiple small files on a server.

Additionally: timeouts due to errors (such as in the case of a bad sector) can cause an SMR drive to be automatically kicked out of a RAID array. They can also cause a RAID array rebuild to fail during “resilvering” (replacing a failed drive).

Even worse: if during resilvering the other SMR drive also encounters an error that causes it to be kicked out, now both of your drives are out, and you are SOL.

If you can’t trust Seagate Technology or WD for your hard drives, whom can you trust…?

Reminders:

1. RAID is not a backup.
2. One backup is none.
3. You need at least one off-site backup.
4. Demand tech specs.