extremely slow delete of files

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cloudwr417h
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extremely slow delete of files

Post by cloudwr417h » Fri Jul 31, 2020 6:53 am

Hello all,
I have a TS809 with QTS 4.2.6, Raid5 with 8 disks, 14Tb total, used 11Tb
Disks are WD Red 60EFAX 6TB disks. I was in the process of substituting the disks from hitachi 2Tb when I hit the 16tb limit.
Indications in the forum are to reset the device, loosing everything in the process, and start with a fresh Raid5 volume.
I'm was in the process of backup/deleting files form the volume when I noticed deletion is extremely slow.
I'm connected in SSH with putty - issuing rm command for each folder once backed-up on external drive.
issue: files over 1Gb of size take between 20 and 30s to be deleted, more if the size is bigger. Smaller files do not exhibit this behavior.
I've disabled the recycle bin, also disabled the antivirus, and for good measure, did a reboot of the nas after disabling the settings.
No other services are running. The files I try to delete are in CIFS shares, but the clients are not trying to access the files anymore.
Besides I see this behavior also in folders that are not shared. During deletion, CPU is between 2 and 3%, ram is at 25% (2Gb total).

I've seen this topic rear its head from time to time over the years, haven't found one that actually identifies the issue - hence the repost.
TIA

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OneCD
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Re: extremely slow delete of files

Post by OneCD » Fri Jul 31, 2020 7:02 am

Hi and welcome to the forum. :)

6TB EFAX are rather unpopular NAS drives, as they use SMR:

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So, all disk write operations (including file-deletion) will be very slow. :(

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cloudwr417h
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Re: extremely slow delete of files

Post by cloudwr417h » Fri Jul 31, 2020 8:21 am

Thanks for the welcome, and for helping out.
True, EFAX is not a Ferrari, then again you get what you pay for :-)
Still this is not the problem I'm facing, for the following reasons:
- EFAX is indeed slower, but I've clocked deleting a 4.7Gb files at over 5 minutes! (real 5m46.377s, user 0m0.001s, sys 0m0.365s). Even if 'rm' would eager zero the file, this is way too much time.
- which comes to my second point: rm only removes references, it doesn't actually destroys the content of the file. The file should've been removed the file in the blink of an eye
- I really only have the problem with deleting files. I'm writing large files at 33MiBs (avg speed for a 8GB file over a 1gbps network)- not great, but enough for my use case), twice faster than the time required for deleting a file of lesser size.

I'm inclined to think it's an issue with the raid controller firmware/driver combination maybe?

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OneCD
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Re: extremely slow delete of files

Post by OneCD » Fri Jul 31, 2020 8:52 am

QTS only uses software RAID (mdadm).

Have you check the IO wait times while deleting? (Easy to do if you install ‘iotop’ or ‘htop’ via Entware).

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