Speeding up a Synology rebuild

After purchasing a Synology NAS I inserted a bunch of drives and left ‘expanding’ overnight.

When I came back in the morning it had gone from 2% to 5% complete – about 95% less than what I was hoping.

I discovered that you can SSH into the box and check the status of the rebuild with:

cat /proc/mdstat

This showed that I had another 14 days left. Hmm, I don’t think so.

After some poking about I discovered it defaults to a strangely small 256 byte cache size.

There were a lot of posts on the internet about changing this value in /sys/block/md3/md/stripe_cache_size, but this failed with a permission problem. Maybe this applied to older versions.

Instead you can edit:


And add the line:


It took a few minutes for this to be picked up and then the rebuild time decreased to 14 hours. Much more acceptable.

I tried some larger cache size values but they didn’t make any difference.


3 responses to “Speeding up a Synology rebuild”

  1. It seems this does not work anymore. Adding md_resync_cache_size to /etc.defaults/synoinfo.conf (the same for /etc/synoinfo.conf) does not change anything. The stripe_cache_size (cat /sys/block/md2/md/stripe_cache_size) is still steadily going back to default 256.
    Any other workaround for this?


    1. I forgot to mention:
      * DSM: DSM 6.1.6-15266 Update 1
      * I did not restart the NAS, just edited the config files and waited (half an hour or so). When setting the stripe_cache_size manually to a higher value it returns to default.


    2. Sorry, I don’t know enough about Synology to help more than what I found above – http://forum.synology.com/enu/index.php is probably a better place.


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