Slow Read and write speeds to cache?

[JeffJeff]

I created a share that uses ONLY uses the cache which is an ssd with approx 500-600MB/s read and write. When transferring a file to and from the share, the first 10-20% of the transfer will do the full speed of the ssd but then falls off to about 120MB/s when writing to and approx 50MB/s when reading from the share. I do have 10gbe using jumbo at 9000 and I am also using windows SMB to transfer the file. I have tested the connectivity between the server and the pc and it will saturate a 10gbe connection so I do not think that is the issue.

 

 

 

unjamie-diagnostics-20200523-1432.zip

[JorgeB]

Initial write speed is high since it's being cached to RAM, then is limited by the device actual write speed, not all SSDs (very few in fact) are capable of sustaining 500MB/s writes, lower capacity models even less likely to do it, announced speeds can usually only be accomplished for low burst writes.

[JeffJeff]

I have enough ram in the system to cache that entire file that I am transferring an I do know that the ssd does have sustained speeds of 550MB/s.

Edited May 24, 2020 by JeffJeff

[JorgeB]

By default only 20% free RAM is used for write cache, after that you're limited by the device, you're also a little limited by network and/or shfs as initial speed should be closer to 1GB/s.