Re: Very high load when reading/writing

[David Sterba <dsterba@suse.cz>]

On Thu, May 01, 2014 at 07:50:11PM +0200, Hendrik Friedel wrote:
> I have very high load when writing/reading from/to two of my btrfs volumes.
> One sda1, mounted as /mnt/BTRFS, the other, sdd2/sde2 (raid) as /
> sda1 is a 3TB disc, whereas the sdd2/sde2 are small SSDs of 16GB.
> 
> I wrote a small script to demonstrate it. It does:
> -echo what it will do
> -show the current load
> -dd from one volume to the other.
> -show the current load
> -sync and flush the cache
> -sleep 300s in order to get the load down again.

load average is not a good metric, it mixes IO an CPU load into one
number, would be better to measure cpu and IO loads separately.

> Here the output:
> Test from /mnt/BTRFS to /tmp
> 124,553 s, 16,8 MB/s

Is the transfer speed comparable if using a bare blockdevice instead of
a filesystem on top of that?

According to the S.M.A.R.T. stats the devices seem to be working
normally.