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I'm having some issues expanding a RAID 5 array on a Synology DS413. The drive has gone from 3 x 3TB WD Green drives to 4 x 3TB. I started an expansion operation and it's been stuck at about 60% and extremely slow speeds for a week (about 350Kb/s when I check /proc/mdstat). I've tried increasing min/max speed limits and stripe_cache_size but it didn't change the actual speed.

The drive is near unusable while the expansion is running, transferring files out maxes out at 400Kb/s. I think the issue is related to bad sectors on Disk 1, when I try and run a SMART test on the drive it gets stuck at 90%.

So because I can't get data out of the disk and the RAID expansion will take over a month, I'm wondering if there's a way to stop the expansion? If I force reboot the disk by disconnecting power, will it corrupt the drives? Are there any other options that people know of?

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    It is likely taking a long time because the system is in use. Disconnect from the network and stop all unnecessary services and you should see the speed increase. Or reboot to single user mode to be certain (mdadm will carry on where it left off). – Paul Nov 17 '14 at 22:50
  • Thanks @Paul - do you think there's any risk shutting it down though with a corrupt/malfunctioning disk? – Tom Maitland Nov 18 '14 at 5:24
  • Bad sectors crop up on disks. Is difficult to assess how big a deal it is. IF the disk was fine, then rebooting isn't an issue. SMART might just be waiting for RAID rebuild to give up the disk so it can do its thing. I would first try and shutdown the synology services (not the whole machine) and see if that helps. What does smartctl -a give you for the disk? Are the 197 and 198 increasing? – Paul Nov 18 '14 at 5:54
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Stopping a simple single disk partition resize is definitely not safe, IMHO stopping a RAID expansion could only be worst.

So, in my opinion: no, stopping a RAID expansion is not safe! (Unless someone at Synology say otherwise)
I don't really know if there is a way to stop it.

If you really need to stop the Raid expansion, try to make a full backup on another Nas/server, no matter if it take 1 month.

If you stop the RAID expansion, consider a total HDD/RAID corruption as one of the possible outcome, and be prepared for it.

You may try to ask also on Synology forum http://forum.synology.com/enu/

About my experience on the matter, I must say than I've never tried to stop a Raid expansion on any kind of server/nas/controller. I've just installed a bunch of simple Raid array in the past, and I'm a happy owner of a Synology DS213j.

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