Backing up to SCSI connected tape library from HyperV host

[HealthyCamper]

Hello,

I'm checking to see what the recommended settings are when using BackupExec on a HyperV VM with a SCSI connected tape library on the host.
Details:
All servers Windows 2008R2 Enterprise FULL (guest and host)
Tape library HP MSL2024 with SCSi Ultrium LTO4 drive
Host NIC Adapters - Broadcom NetXtreme
Guest running BackupExec 2012 with Symantec tape drivers installed
Host using HP tape drivers to get tape and library to appear from presentation via iSCSI
Latest version (at time of writing) of Starwind Tape Redirector

I've had a few issues with getting the library and drive to be recognized post boot, but this seems OK now - the only issue I have is the actual through-put. As the guest is connecting to the host via the internal VMBus, I wouldn't have through that network speed would be an issue put maybe it is and I'm down to about 20% of the throughput I did have with the same hardware.

Pre Virtualisation throughput - 4500 MBps, post virtualisation throughput 980 MBps

Any tips or things I should check to improve the performance?

[Max (staff)]

Hi HealthyCamper,
Sorry but I have to copy over my spiceworks post, the steps I've provided are first on the performance checklist anyway.
Microsoft iSCSI Initiator properties:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4d36e97b-e325-11ce-bfc1-08002be10318}\0001\Parameters\

MaxRecvDataSegmentLength 524288

MaxTransferLength 524288

FirstBurstLength 524288

MaxBurstLength 524288

After that you need to modify the appropriate parameters in the Tape Redirector (Select server->Configuration Tab->Advanced settings)

Please let me know if this helps,

[HealthyCamper]

Thanks, I'll let the current full-backup complete (23 hours and counting, but at least we're verifying now!) and then try those.

So are those settings on just the client or on the host as well?

Also, do they require recreating target, restarting services or servers for that matter?

I'm in Spiceworks too (same handle) so I'll check there too.

[Max (staff)]

These settings are applied on both sides.
Registry changes on the client require system restart, StarWind changes may require StarWind service restart.
PS: I'm active in the same thread on Spiceworks

[HealthyCamper]

HI Max,

Had already started the next backup before I saw your next post, so had applied reg settings to client only (NB: applied these values as HEX, not Decimal - is that right?) and restarted iSCSI services. Restarted starwind services on Host after settings values (could only set 3 of the 4)

Speed now up to about 1700 Mbps so approximately doubled = good start.

Am I right in thinking that the NICs themselves are NOT actually in use as all the traffic is passing over the Virtual switch and therefore not hitting the NICs at all? Neither device shows any bottleneck on the network at any rate.

So my next move is to apply the same REG settings to the host iSCSI parameters, restart services and test again?

[Max (staff)]

you don't need to modify the REG entries on the Host OS side - these only have effect on the machine where you run iSCSI initiator to connect to the tape.
So it's StarWind tape redirector service restart from the hyper-v host and VM restart to apply the reg changes.