Speed going down

[Archaniel]

Hi,

I'm currently uploading quite a lot of data to my NAS and I noticed that the disk IO speeds (and upload speed aswell) were slowly and steadily going down while copying movies (700MB+ files)

at 18:55 transfer finished.

Can somebody explain, why is this happening please?

 

[Archaniel]

oh, my setup is here https://forums.freenas.org/index.php?threads/1st-freenas-build.44759/

 

[cyberjock]

A slow decline is normal as disks read outer sectors faster than inner ones.

 

[Archaniel]

but that much ? This means that the space is being eaten up from "outside". Also I've written about 2TiB from, meaning I can expect another 15MB/s decline in write speeds as I'm going to fill up the drive? Can't I tune it somehow? I don't like that idea :/

Also, I don't know how free space is being calculated...

I have 5x 3.0TB drives in raidZ2 - Basically the parent "Storage" is 3.8TiB + 9.8TiB = 13,6Tib. Which is all 5 Drives summed up together
The first child "Storage" says 2.2TiB + 5.6TiB = 7.8TiB, but while the storage was empty, the "available space" was 8,16TiB (which would correspond 3/5 * 13,6)

or is that those 1.4% which ZFS uses for metadata?

 

[cyberjock]

Many disks decrease in speed by 50%. So yeah, totally normal and not much you can do about it. There is no tuning this as the issue is the physicality of you accessing the data. If you don't want the slowdown then buy an all-SSD setup. Scratch that, buy 2 so you can send me one.

This behavior is why people "short stroke" platter disks.

 

[Robert Trevellyan]

or is that those 1.4% which ZFS uses for metadata?

Yes, there is overhead with ZFS, as will all filesystems.

 

[SweetAndLow]

your source you are copying from could also be slowing down.