Sawtooth write speeds?

[w5lee]

Hello, I am seeing write speed vary when moving large files. Any ideas why I am seeing this behavior? It happens both to cache and array writes.

 

 

 

Edited February 11, 2018 by w5lee
remove second image

[tdallen]

Hi -

 

How much memory do you have in your system, and what are you writing to?

[tbonedude420]

First thing I notice... is faster then normal speeds... are you using any kind of nic bonding? If so, the source your reading from, *seems* to be saturating the connection, but the other side (server side) cannot handle such input... there for the sawtooth pattern.

 

Could you comment more on the sending and receiving sides as far as physical hardware, specifications, and disk speed/network speed stats?

 

I ask though, because I've experienced this exact same thing, but my issue was due to my sending side, and network being beefier then the ending destination, creating exactly the same pattern your seeing. 

[w5lee]

Thanks for the responses. I need to check my forum settings as I didn't get an email my post was replied to so sorry for the delay.

 

My system has 32GB of memory. I am writing to a cache pool of 3 SSD's using btrfs.

 

The data is not using the network the copy is being done on the server. I found a nice youtube video on configuring a root share to move data from one place to another without having to move data over the network.

This works great! He has many other well done and informational videos as well. Check them out!

 

So bottom line this is moving data from one share on the cache pool to another one. I would expect a fast transfer. Looks to me it first copies to ram. Once the ram is exhausted then it flushes to disk. Maybe that is what is causing the sawtooth. I would like to figure it out and try to fix as the transfer rate goes to zero sometimes and just seems to hang there a bit. Then things take back off again. Think it is a config issue but not sure.

 

[JonathanM]

7 hours ago, w5lee said:

I am writing to a cache pool of 3 SSD's using btrfs

Are the SSD's regularly trimmed?

Is the btrfs pool healthy?

[pwm]

I have several times seen the exact same oscillating bandwidth when copying using remote desktop from one Windows machine to a USB drive connected on another Windows machine. It seems like Windows have some bandwidth-controlling or RAM-buffering code that can become unstable in some situations.

[w5lee]

I am not sure about the SSD's being trimmed

Pool appears healthy no alerts anywhere

Side note if I move a large file to the array I see the same sawtooth behavior, just at a much slower throughput.

 

PWM: The data isn't moving to the windows machine. I have verified this by using task manager and looking at my network bandwidth and can confirm the data isn't going through my windows box.

[w5lee]

Here is an example of copying from two array shares. I am showing the resource monitor to demonstrate data isn't going through my windows box:

[Vr2Io]

"Sawtooth write speeds" in unRAID may be common.

 

For this case, if the file not in same disk, even transfer not through Network, it still need time to complete the transfer between disks.

 

Could you make some calculation i.e. file size / time spend, then you will got actual transfer speed.

Edited February 13, 2018 by Benson

[lukesaber]

I too have the sawtooth data transfer speed problem.

Happens when copying to and from the array over network connection.

 

I suppose i could try replacing the NIC in the array (unraid is really sensitive to NIC's in general)

I would love it to be something to do with a setting.

 

Literally, the transfer speed peaks at 70 megs a second then drops to zero, then picks back up to 70.... over and over again.

I'd be happy for a stable 50.

 

is there some tool to test bus speeds and transfer rates for devices in the unraid rig?

[lukesaber]

posting again with reply notification on... i'd like to track this thread