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Tape Redirector speed issues

Tape drive and auto-loader redirector (iSCSI)

Moderators: art (staff), anton (staff), Anatoly (staff), Max (staff)

Tape Redirector speed issues

Postby PeteMartell » Mon Mar 25, 2019 9:11 am

Greetings,

I started using StarWind Tape Redirector to get my Quantum Scalar i40 fibrechannel tape library (LTO6 drive) attached to my Windows Server 2012R2 based Veeam VM running in a Hyper-V Cluster (2012R2 Hosts). The VM is connected to a gigabit network port and can put the gigabit through to the Tape Redirector host and other devices in the network. Using HPE Library and Tape tools on the physically attached redirection host I get 170 megabytes per second to the tape, on my virtual machine the speed is somewhere between 30-37 megabytes. Tape Redirector is attached with the iSCSI initiator and i already tried setting the MaxTransferLength regkey to 64KB (rebooted of course) with no positive effect and tried enabling Jumbo Frames (9k) on my virtual network adapter, also no real benefit. The physical network port does nothing besides being there for the Veeam machine and the VM had no other traffic during tests, so the load on the vNIC is around 38 megabytes also.
I've read through most other speed issue threads and I can live with this problem for now, using Veeam "forces" me into the d2d2t scenario anyways, but you might have another tip for me? I might try using a 10gbit port, but my hopes that something changes are low.
Since the problem couldn't be solved for most other people on this forum, where does it stem from? Is it something that might be fixed in future releases?

That being said, thanks for providing us with your pretty easy to use tool for free, it's heaven send, even with the speed issues.
PeteMartell
 
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Re: Tape Redirector speed issues

Postby Oleg(staff) » Wed Mar 27, 2019 4:34 pm

Greetings,
Could you please clarify, what StarWind build are you using?
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Re: Tape Redirector speed issues

Postby PeteMartell » Thu Mar 28, 2019 1:22 pm

Hey Oleg,

Console shows as 8.0.0.12767
The UI plugins as just 8.0
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Re: Tape Redirector speed issues

Postby PoSaP » Fri Mar 29, 2019 10:49 am

Hey Pete,
Did you check the connection speed with the help of, for example, iperf?
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Re: Tape Redirector speed issues

Postby Oleg(staff) » Fri Mar 29, 2019 11:02 am

Yes, please check actual network speed.
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Re: Tape Redirector speed issues

Postby PeteMartell » Fri Mar 29, 2019 3:19 pm

Hello to you both,

yes, I tested it. As I initially mentioned, the VM that has the tape speed issues is connected to a dedicated gigabit port that no other VM or the host itself uses and can put around 120mbytes/s through - measured with a fsutil dummy file - to the host it resides on/tape redirector and different other places in the network. I initially had those problems with VMQ or what's it called, but now the actual gigabit is in use.

Greetings and have a nice weekend
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Re: Tape Redirector speed issues

Postby anton (staff) » Sun Mar 31, 2019 3:50 pm

The problem is not with your network, but with a way SPTI (SCSI Pass Thru Interface) works within Windows operating system. It's synchronous regardless of what, so before one command isn't completed by I/O Manager, caller is "frozen" and can't issue more commands (reads or writes or whatever).
This is what dramatically slows down everything. In theory we could use custom driver to handle SCSI traffic (and we even did it ourselves and licensed advanced SPTD stack from Disc Soft, same code used by Daemon Tools guys). In general it helps but it affects potential stability and... to be honest, there's no much market for such a solution,
so we prefer to give it away free of charge and invest time (also minor) into VTL stack. Veeam guys have a point when they push Disk-to-Disk-to-Tape (D2D2T) scenario.

PeteMartell wrote:Greetings,

I started using StarWind Tape Redirector to get my Quantum Scalar i40 fibrechannel tape library (LTO6 drive) attached to my Windows Server 2012R2 based Veeam VM running in a Hyper-V Cluster (2012R2 Hosts). The VM is connected to a gigabit network port and can put the gigabit through to the Tape Redirector host and other devices in the network. Using HPE Library and Tape tools on the physically attached redirection host I get 170 megabytes per second to the tape, on my virtual machine the speed is somewhere between 30-37 megabytes. Tape Redirector is attached with the iSCSI initiator and i already tried setting the MaxTransferLength regkey to 64KB (rebooted of course) with no positive effect and tried enabling Jumbo Frames (9k) on my virtual network adapter, also no real benefit. The physical network port does nothing besides being there for the Veeam machine and the VM had no other traffic during tests, so the load on the vNIC is around 38 megabytes also.
I've read through most other speed issue threads and I can live with this problem for now, using Veeam "forces" me into the d2d2t scenario anyways, but you might have another tip for me? I might try using a 10gbit port, but my hopes that something changes are low.
Since the problem couldn't be solved for most other people on this forum, where does it stem from? Is it something that might be fixed in future releases?

That being said, thanks for providing us with your pretty easy to use tool for free, it's heaven send, even with the speed issues.
Regards,
Anton Kolomyeytsev

Chief Technology Officer & Chief Architect, StarWind Software

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Re: Tape Redirector speed issues

Postby PeteMartell » Mon Apr 01, 2019 2:36 pm

Hey Anton,

thanks for the professional answer. It's always nice to read your well explained posts. In a theoretical scenario, what's the limiting factor of the SPTI function? Does it simply come down to unavoidable latencies or could I achieve better performance by throwing redirected hardware at the guest machine if need be?
PeteMartell
 
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Re: Tape Redirector speed issues

Postby anton (staff) » Wed Apr 03, 2019 3:33 pm

It's operational latency so going faster tape drive might help, but... I'd stick with a VTL as a middle man as that's a production scenario.

PeteMartell wrote:Hey Anton,

thanks for the professional answer. It's always nice to read your well explained posts. In a theoretical scenario, what's the limiting factor of the SPTI function? Does it simply come down to unavoidable latencies or could I achieve better performance by throwing redirected hardware at the guest machine if need be?
Regards,
Anton Kolomyeytsev

Chief Technology Officer & Chief Architect, StarWind Software

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anton (staff)
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