Poor speeds to LTO-5 Tape Drive

Question

I have a new server connected with 8gb Fibre to a Dell TL2000 with an Lto5 drive(IBM LTO-5 Drive). For testing I am pulling directly from an ISCSI device that is using 3 NIC's in MPIO. I can successfully pull 230-250MBps from this Array.
However, The tape is only writing at between 50-60MBps. I can monitor the speed with the Fibre Channel utility. The queue length never exceeds 1.  Also the Nic's never exceed 25% utilization and When I create a large copy form the array I can easily
exceed 80% on all of them(when I am going at 250MBps)
CPU does not exceed 5% with 8 cores remaining parked and I still have 8gb of memory free.
So why can DPM not utilize the full bandwidth to feed the LTO5 drive? I need to feed the drive at over 200 so I can get into streaming mode and avoid shoeshinning the tape.
Thanks,
Nick

Answer 1

Hi,
We have tools that mimick the way that DPMRA reads from disks and writes to tapes to try to narrow down where the problem is.  
DPMRA reads from a disk shadow copy and we have a tool that mimicks disk reads from a folder and shows disk read speeds in real time.
c:\>DPMFileIoPerf.exe -testIR -sourcedir "V:\Virtual machines\SMBEX01" -usesnap
Creating Snapshot for Volume : V:\
Snapshot Created Successfully :
\\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy6\
Starting DPM IR test...
I/O Speed:[67] MB/Sec;
I/O Speed:[71] MB/Sec;
I/O Speed:[69] MB/Sec;
I/O Speed:[67] MB/Sec;
I/O Speed:[67] MB/Sec;
I/O Speed:[66] MB/Sec;
I/O Speed:[66] MB/Sec;
I/O Speed:[66] MB/Sec;
I/O Speed:[63] MB/Sec;
I/O Speed:[63] MB/Sec;
I/O Speed:[63] MB/Sec;
I/O Speed:[63] MB/Sec;
Total Bytes Processed:[15739301352], Average I/O Speed:[66] MB/Sec;
Completed DPM IR test...
DPMRA writes and reads using 64K block size and 192K buffer size and the tape tool does the same to see what the raw write and read speed of the tape drive.
example of output:
C:\>tapeioperf \\.\Tape2147483646 64 192 1000 2
Status: Getting the handle for the tape \\.\Tape2147483646 ...
Success
Status: Setting Tape Information...
Success
Status: Loading the tape...
Success
Writing...[1]
Status: Writing ...
Block Size              : 64 KB
Buffer Size             : 192 KB
Number of Bytes written : 999 MB
Time Taken              : 8221 ms
MegaBytes/Second        : 121.518063
Writing...[2]
Status: Writing ...
Block Size              : 64 KB
Buffer Size             : 192 KB
Number of Bytes written : 999 MB
Time Taken              : 8159 ms
MegaBytes/Second        : 122.441476
Status: Rewinding Tape ...
Success
Reading...[1]
Status: Reading ...
Block Size              : 64 KB
Buffer Size             : 192 KB
Number of Bytes Read    : 999 MB
Time Taken              : 8938 ms
MegaBytes/Second        : 111.769971
Reading...[2]
Status: Reading ...
Block Size              : 64 KB
Buffer Size             : 192 KB
Number of Bytes Read    : 999 MB
Time Taken              : 9032 ms
MegaBytes/Second        : 110.606732
So, obviously, the bottleneck in the above test shows we have slow local disks, so we would never achieve greater throughput than the disk reads.
If you open a support case with us we can run the tools on the DPM server to get disk read and tape write speeds to see what is happening.
Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Regards, Mike J. [MSFT]
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