04-20-2011 01:09 PM
Hello,
There is a problem that appears to be related to hardware compression, as the "throughput" of the job (the MB/sec) seems to be cut in half from ~800MB/sec to ~400MB/sec.
This has been occuring for several months (as reported by the site).
I have found an interesting article on using the tracer.exe tool to identify if the tape drive is being set to full compression: http://www.symantec.com/business/support/index?page=content&id=TECH50960
When I trace the conversation between backup exec and the tape drive the following results are found:
--Backup exec job tracer.exe log:--MODE_SELECT6 (sends commands to hardware)Data byte 5: 0F = Data Compression Page is being modifiedData byte 7: C0 = Data Compression is being turned onMODE_SENSE6 (response from hardware)Data byte 5: 44 = not goodData byte 7: 00 = Data Compression is being turned offMODE_SELECT6 is sending the proper command, but MODE_SENSE6 is returning that a value indicating that hardware compression is off.
--HP Tape Tools Data compression test tracer.exe log:--MODE_SELECT6 (sends commands to hardware)Data byte 5: 44 = not goodData byte 7: 00 = Data Compression is being turned offMODE_SENSE6 (response from hardware)Data byte 5: 44 = not goodData byte 7: 00 = Data Compression is being turned off
04-20-2011 01:38 PM
are you using the Backup Exec Device drivers ?
Is the data being backuped from the local (backup exec) server or a remote server ?
Because if the data has to be copied over the network and it cannot be delivered fast enought your speed will never be the same as the HP LTT. HP LTT generates it's own data to backup so it is always streaming at maximum speed.
04-20-2011 02:08 PM
Self,
HP said to perform the following with tape tools to manually flash the latest firmware and switch on the hardware compression
In addition to the above tracer.exe trace, you may want to look into sgmon: http://www.symantec.com/business/support/index?page=content&id=TECH50766
04-20-2011 02:09 PM
Yes, I just changed these drivers last night. Before (after a proliant support pack install), the Symantec drivers weren't being used, but HP's.
Thanks!
Matt
04-20-2011 06:13 PM
Why do you say that hardware compression slows down your throughput? Are the figures quoted obtained when you have turned hardware compression off and on respectively? Could there be some other reason for the slowdown?
Other than the hardware compression angle, you might want to look at tuning your tape drive buffers. See my article below.
https://www-secure.symantec.com/connect/articles/tuning-my-lto4-tape-drive
04-21-2011 07:06 AM
Thanks. I'll look into this later, but for now, it appears that the throughput of "data" stored on the tape (as in how many MB/sec of data the tape can write) is half of that of another machine with the same exact hardware and driver configuration.
However, I estimate that due to my findings, there is a problem with the signalling, and that it isn't a buffer "issue" that a tweak can fix. However... the more performance the better!