Transfers slower as drives getting close to full

[bally12345]

I think I know the answer but just wanted confirmation. Is it normally for transfer speeds to get slower as the disks get close to full?

 

Reason I ask is when I added SSD cache I was getting 110MB/s from local windows machine to unraid but now all my disk are ~90% full and speeds have dropped to around 40MB/s sometimes bursting to ~70MB/s

[trurl]

What filesystem? ReiserFS is known to have some performance degradation as drives fill up.

[danioj]

I think I know the answer but just wanted confirmation. Is it normally for transfer speeds to get slower as the disks get close to full?

 

Reason I ask is when I added SSD cache I was getting 110MB/s from local windows machine to unraid but now all my disk are ~90% full and speeds have dropped to around 40MB/s sometimes bursting to ~70MB/s

 

To answer your initial question, the short answer IMHO is yes, it is expected.

 

As I understand it, writes to a nearly empty drive are appreciably faster than those to a full drive, since it's the writes are going to be on the outer cylinders of the drive, which typically has data transfer speeds more than double those of the inner cylinders.

 

An option for you here is to balance the data across the drives either using the "most free" fill method or by manually balancing the data across the drives (if they are already full).

 

If you uniformly balance all the writes then the overall performance will degrade uniformly as the array fills up.

 

There is a tool to use which will help you balance the data on your disks (if you want to do it) and I cannot recommend it enough, unBalance.

 

https://lime-technology.com/forum/index.php?topic=45352.0

 

Note: credit @garycase for the majority of this information.

[bally12345]

@trul Yep I still have some drives are still ReiserFS from when I was using v5. I dont have enough space to move the data off the drives and reformat 

 

@danioj Thanks for the info will take a look at unBalance

 

Just thinking about it though, all my shares have cache enabled and write to SSD cache fist so should I be getting slow down? I do have SSD Trim installed.

[trurl]

Is your cache RFS also? How full? If cache gets too full or if you're updating files that are already on the array cache will be bypassed.

[bally12345]

Cache is btrfs and I have mover set to every 8 hours so usally the cache is clear but it has been ages since I have seen full speed transfers. Maybe I should run speed check on each disk to rule out any other issues.