Write vs Read Speed on Cache Drive


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I have read many threads on here for slow read speeds, but can't seem to resolve this issue.

 

I can write a large file to my 7200 RPM cache drive (from an SSD drive on  my laptop) at over 100MB/s. However, when I read the exact same file back to the same SSD on the laptop, it averages at 30MB/s. Same network card, same switch, same everything as far as I can tell. The SSD on the laptop can be written to very fast (180MB/s) testing from another SSD hooked up via USB3.

 

Reading from other drives in the data array I get similar read speeds. I know writing to the array will be much slower since parity is being updated during the write.

 

Diagnostics attached, in case it would help.

 

Thanks for any direction you can offer!

PTM-unraid-diagnostics-20170322.zip

SSD to Cache.png

Cache to SSD.png

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I had an issue which had similar symptoms, What I found was that I had an out-of-date NIC drivers for Win7.  For details, look at the following quote which was in this thread:

 

   https://forums.lime-technology.com/topic/53172-windows-issues-with-unraid/#comment-515643

Quote

<<<snip>>>

In my own case, I have reverted my Test Bed server back to 6.1.9 because of SMB issues copying files off of the server.  (I thought I had it 'fixed' when I switched to using Explorer++ as a Windows file manager but that started giving me problems.  My gut feeling is that the issue is on the Widows end of the equation but I can't quite put my finger on what triggered it.)  Johnnie.black posted up about what he found in a series of posts in this thread:

 

      http://lime-technology.com/forum/index.php?topic=53689.msg516457#msg516457

 

[EDIT:  I finally isolated the problem of slow copies off from the server to my Win 7 computers.  It was an out-of-date Windows NIC chipset driver for a RealTek NIC.  I downloaded an updated driver from the Motherboard manufacturer and that seems to have fixed the problem. ]

<<<snip>>>

 

If you read my complete post, you will find that Samba/SMB issues with similar symptoms will have different solutions.  The "Windows Issues with unRAID" thread is a good starting point.

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1 hour ago, johnnie.black said:

See if this helps:

 

 

 

Thanks - I had seen that in the FAQ before, but for some reason it didn't click to try that. I did make the change and it increase read performance a bit - not still not close to the write speeds. Bumped it up to about 50MB/s.

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One more thing.  You might want to try LAN Speed Test (google for it) by Totusoft.  It has the advantage that eliminating any overhead introduced by a file manager on the PC end.  After you are sure it works, be sure to use file transfers in the 5GB or larger to eliminate the RAM buffering on the unRAID side.  It also waits for the file to close on the unRAID end before it calculated the transfer speed.  (A lot of file managers use just the time required to finish the transfer to the network without considering any buffering occurring on the other end.)

 

My write speeds to my Test Server was 67.882,048 MBps (directly to the array using 'reconstruct write') and from the server was 114.819,459 MBps. 

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Have you tried another computer for the same tests?  Have you check to see that you have the latest NIC drivers for your laptop? 

 

The reason that I am saying this is there are not many complaints about reading speeds on the forum and I know that I had an issue that I struggled with for a month that I finally determined was caused by the RealTek NIC drivers on THREE computers.  (I am one of those who doesn't update drivers unless I have a problem!)

 

I also noted that you are using a mapped drive, you might want to check the speed by going directly to the server.  Just use the browse dropdown button on the end of the 'Folder or server IP' line and navigate down the Network icon.  It would be interesting to see if the speed is different. 

Capture.JPG

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