Terrible write performance


New Around Here
I've got a QNAP TS-431X connected via 10 GbE and filled with 3x 18 TB drives in a RAID 5 array.

The problem: At best I get 60 MB/s write speeds, usually it is around 30 MB/s though. Read speeds are ok, with 300+ MB/s. The CPU is rather bored in all of this. I noticed that a ton of reads happen when writing files, and the drives are making lots of seeking noises.

Is this normal or is something going terribly wrong? And if so, does anyone have a clue what it could be or what I could do to figure it out?


Very Senior Member
You should check out the QNAP community forum.

Many things to check including antivirus.

What are you using to determine the actual write speed vs a network, client issue?


New Around Here
There are slower USB drives attached to the NAS, and write speeds are much faster to it (can max out the 160 MB/s). Also, before I went to RAID 5, I had to start with a single drive for space reasons. That could be filled at much higher speeds. As I did not pay much attention I'm not sure, but I believe I saw up to 300 MB/s. Since then the only thing that changed was adding a drive, switching to RAID 1, and then another drive and switching to RAID 5. I did not install any more packages. iperf3 is giving me around 600 MB/s between my desktop and my NAS. Also, the client reads the data to be sent much faster than the NAS can write it, so it fills up the cache and then slows down. The client shouldn't be the issue, IMHO, especially since sending data to other drives connected to the NAS works much faster. The integrated benchmark feature of QNAP claims 210 (WD) or 260 MB/s (Toshiba) read speeds per drive.

I tried to deactivate the malware remover. Apart from that, not much is installed. There is no Multimedia Console for example, which would index photos etc. Qsirch isn't installed either. The NAS has 4 GB of RAM.

Perhaps the mistake was to leave one of the old drives in the NAS to keep the settings while creating a new array, so something was messed up (the NAS did not migrate all the packages I had installed previously to the new array).

I did however do a factory reset when I noticed the performance issues and couldn't figure out what was causing trouble, alas with no effect.

If I knew that it will perform better if I start fresh I'd buy another 18 TB drive, as I do not have the space at the moment.
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Part of the Furniture
3x 18 TB drives in a RAID 5 array

There's your problem right there - RAID5 can read fast, but writes are limited to the speed of a single drive. RAID10 will get you much better write performance - but there you'll need one more disk in the array, 4*10, and you'll have half of that available for storage (the other half is redundancy).

Put another disk in, nuke and rebuild the array from scratch with current QTS (yes, that matters)... and again, strongly consider RAID10 over RAID5 (RAID5 is the second most risky version of RAID after RAID0 - mostly due to failures during the rebuild on a disk element replacement)

The TS-431X is a dual-core Annapurna Labs AL212 @ 1.7GHz - 32-bit ARM, and the A15 is comparable to Intel Atom from 10 years ago...

Other things to look at...

enable SMB3, with min version of SMB2 - IIRC, the default is not to enable SMB3 on the ARM variants, also look at Async I/O, but that comes with some risk of data loss if power is cut (async I/O is deferred writes).

I don't recommend using external drives via USB as part of your storage set - they're good for backups, but not as primary storage.

good luck...

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