Friday, September 24, 2010

Linux Enable Write-Caching On Disk

When booting a VM recently, I received the error message below regarding I/O writecaching & virtual hard disk corruption:

After Googling for a bit, I found that the first thing to check with this error is whether I/O write caching is enabled on the VM.  In my case, it was.

Next, a lot of the posts I was reading were stating the corruption was occuring on "ext4" partitions.  I assumed that the write caching was a filesystem option.  I had heard of the disk write cache when working on Windows servers, but never really knew the specifics. 

After a bit more research, I found disk write-caching was actually a drive option that could be set with the hdparm command.  It will improve performance by 10-20%, but can also cause system instability. 

To enable write-caching on the drive, I ran command:

[user@box ~]$ sudo hdparm -W1 /dev/sda

 setting drive write-caching to 1 (on)
 write-caching =  1 (on)

And rebooted the machine, effectively taking care of the error.

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