Monthly Archives: December 2018

Super slow write speeds to Synology DS414

By   December 2, 2018

I was successfully running my DS414 with a combination of 4TB+4TB+4TB+1.8TB disks in two volumes.  I wanted to increase capacity so I bought a 6TB seagate external disk because the price was right.  I figured I’d pull the disk out of the chassis and slide it into my NAS.  Mistake number one.

The disk inside the chassis was a Seagate ST6000DM003.

After waiting 3 weeks for the volume to resize I started using the Volume.  My plan was to move some ProxMox containers and VM’s onto the Volume as part of a PVE update.  But any reads/writes to/from the volume would cause the entire volume to lock up for 30 seconds at a time.  This was causing Plex streaming to block as well. Something was wrong.

I used the Synology tools to try to figure it out but there was no help there.  So I did what I do best and dove into the shell.  I ssh’d and started digging around.   After some digging, here is what I discovered.

Here’s the configuration:

/dev/sda – Seagate ST4000DX001

/dev/sdb – Seagate ST4000DX001

/dev/sdc – Seagate ST6000DM003

/dev/sdd – Western Digital WD40EZRX

/proc/diskstats showed that the weighted average IO completion time for the ST6000DM003 was 160x slower than the other disks:

sh-4.3# cat diskstats | grep ” sd[abcd] ” | awk ‘{print $3,$14}’
sda 5628640
sdb 5558600
sdc 946825590
sdd 5950130

I have a bad disk.

The more bad news is that Seagate’s website doesn’t appear to be able to pull up the warranty status because the disk serial number is not found on Seagate’s side.  I probably have to get the serial number of the chassis.  This probably implies that Seagate is not going to honor the disk warranty because I pulled it out of the chassis.   I’ve sent a support request so we’ll see what I get back on that.