Split from FAQ for unRAID v6

On 6/30/2019 at 11:26 AM, Squid said:

Fix Common Problems is telling me that Write Cache is disabled on a drive.  What do I do?

 

This test has nothing to do with any given unRaid version.  For some reason, sometimes hard drive manufacturers disable write cache on their drives (in particular shucked drives) by default.  This is not a problem per se, but you will see better performance by enabling the write cache on the drive in question.

 

To do this, first make a note of the drive letter which you can get from the Main Tab

 

 

Then, from unRaid's terminal enter in the following (changing the sdX accordingly)

 

hdparm -W 1 /dev/sdm

You should get a response similar to this:

/dev/sdm:
 setting drive write-caching to 1 (on)
 write-caching =  1 (on)

If write caching stays disabled, then either the drive is a SAS drive, in which case you will need to utilize the sdparm commands (google is your friend), or the drive may be connected via USB in which case you may not be able to do anything about this.

 

99% of the time, this command will permanently set write caching to be on.  In some rare circumstances, this change is not permanent, and you will need to add the appropriate command to either the "go" file (/config/go on the flash drive), or execute it via the user scripts plugin (with it set to run at first array start only)

 

It should be noted that even with write-caching disabled this is not a big deal.  Only performance will suffer.  No other ill-effects will happen.

 

NOTE:  If this does not work for you, then you will either need to contact the drive manufacturer as to why or simply ignore the warning from Fix Common Problems

 

I tried the command hdparm -w 1 /dev/sdm but it didn't work, there is a slight typo, you have to remove the space between the W and 1 .  The command should be.

hdparm -W1 /dev/sdm

I found a great resource for hdparm commands here with detailed descriptions and when its best to turn disk cash on and off.   https://www.linux-magazine.com/Online/Features/Tune-Your-Hard-Disk-with-hdparm