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ATTN: SPTI mode (especially for tape drives sharing)

Tape drive and auto-loader redirector over iSCSI

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ATTN: SPTI mode (especially for tape drives sharing)

Postby anton (staff) » Sun Sep 02, 2007 7:41 pm

Ladies and Gentlemen,

SPTI mode is a little bit nasty... Biggest problem with it - local access to the device has I/O buffer size limit. For Serial and Parallel ATA devices it's usually up to the 128KB. As remote site has no idea about this limit size it's quite possible it will issue transfer sizes LARGER then device can accept. Microsoft iSCSI initiator has buffer size of the 256KB by default. This brings us into the situation when we just cannot complete the request b/c local device requests it! For the hard disks Windows breaks everything into the 64KB packets so in 99.9999% of the cases you'll not hit this but for tapes and CD/DVD media apps talking to the redirected hardware try to use as large requests as they can. This leads us into the trouble... As we cannot break single transfer into smaller ones on the target side (this will break command sequence...) the only way to solve the issue is to limit request size on the initiator side.

For the Microsoft iSCSI initiator registry value is:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E97B-E325-11CE-BFC1-08002BE10318}\{...}\Parameters]
MaxTransferLength DWORD = 0x10000

and for Rocket Division Software StarPort the value is:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Services\StarPort\Parameters]
MaxBufferSize DWORD = 0x10000

Please reboot after applying changes. After this everything should work fine :)

Thanks!

Anton
Regards,
Anton Kolomyeytsev

Chief Technology Officer & Chief Architect, StarWind Software

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Re: ATTN: SPTI mode (especially for tape drives sharing)

Postby mprowe » Tue May 20, 2008 9:49 am

anton (staff) wrote:and for Rocket Division Software StarPort the value is:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Services\StarPort\Parameters]
MaxBufferSize DWORD = 0x10000


Hi Anton,

Only a minor point, but I think the path given may be wrong?
There is a \control\ to many! I think it should be:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\StarPort\Parameters]

Martin (the pedant!)
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Re: ATTN: SPTI mode (especially for tape drives sharing)

Postby anton (staff) » Tue May 20, 2008 4:05 pm

My one is correct.

mprowe wrote:
anton (staff) wrote:and for Rocket Division Software StarPort the value is:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Services\StarPort\Parameters]
MaxBufferSize DWORD = 0x10000


Hi Anton,

Only a minor point, but I think the path given may be wrong?
There is a \control\ to many! I think it should be:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\StarPort\Parameters]

Martin (the pedant!)
Regards,
Anton Kolomyeytsev

Chief Technology Officer & Chief Architect, StarWind Software

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Re: ATTN: SPTI mode (especially for tape drives sharing)

Postby Robert (staff) » Thu Sep 03, 2009 12:55 pm

Sometimes the values of MaxBufferSize may be different from TrueMaximumTransfer value of your tape device and may be not 65536 (0x10000);

In order to find out what's really the Transfer Size that your tape can accept, you can do one of the following:

1. Use Any SCSI Persistent Reservation Test Utility (I used PResTest v 1.0) on the target side (PC where a tape device is connected) and check what is the transfer size that your tape can accept, i.e.:

SCSI PR test tool v 1.0

***** STORAGE ADAPTER DESCRIPTOR DATA *****
Version: 00000020
TotalSize: 32
MaximumTransferLength: ffffffff (bytes)
MaximumPhysicalPages: 00000010
TrueMaximumTransfer: 0000f000 (bytes)
AlignmentMask: 0
AdapterUsesPio: False
AdapterScansDown: False
CommandQueueing: True
AcceleratedTransfer: True
Bus Type: Scsi (1)
Bus Major Version: 0002
Bus Minor Version: 0000

...and set the MaxTransferLength or MaxBufferSize on the Initiator side to 61 440 (0x0000f000) as Anton explained.
Remeber to run the PR test on the target side (on the PC connected to tape drive) with SPTI device removed from StarWind Console.

2. The other way - is simply set the transfer rate to a lower value in the settings of your Backup software (BackupExec or DPM)

Thanks
Robert
StarWind Software Inc.
http://www.starwindsoftware.com
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Re: ATTN: SPTI mode (especially for tape drives sharing)

Postby MBerthe » Wed Nov 18, 2009 6:22 pm

Hi,
Where is it possible to get PResTest v1.0 ?
I would like to check TrueMaximumTransfer on some system for improve performance.
Thanks a lot.
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Re: ATTN: SPTI mode (especially for tape drives sharing)

Postby anton (staff) » Thu Dec 09, 2010 9:26 pm

Could you please write to support@starwindsoftware.com and we'd be happy to help. Thanks!
Regards,
Anton Kolomyeytsev

Chief Technology Officer & Chief Architect, StarWind Software

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Re: ATTN: SPTI mode (especially for tape drives sharing)

Postby sanel » Tue Nov 01, 2011 11:57 am

Someone knows how to check TrueMaximumTransfer? Where is it possible to get PreTest v1.0
Last edited by sanel on Fri Jan 20, 2012 9:24 am, edited 1 time in total.
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Re: ATTN: SPTI mode (especially for tape drives sharing)

Postby anton (staff) » Tue Nov 01, 2011 1:09 pm

Please check values corresponding to registry keys mentioned above. That's easiest way to go.

sanel wrote:Someone knows how to check TrueMaximumTransfer? Where is it possible to get PreTest v1.0
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