08-14-2013 07:51 AM
According the the Netbackup tuning guide, the size of shares data buffers UNIX should follow the following guideline:
64K for tapes
256K for disk
In a case where we have a VTL. I assume that the virtual tapes are considered as normal tapes for netbackup. So SIZE_DATA_BUFFERS is the value taken for the virtual tapes instead of SIZE_DATA_BUFFERS_DISK. But should virtual tapes not be treated as disks?
And if I consider to treat it as disk, the value I have to put would need to be 256K in the SIZE_DATA_BUFFERS. And then what if I need to set the value for real physical tapes?
Thank you in advance for considering my question.
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08-14-2013 08:39 AM
I'm using 256K for all modern tape devices including VTL. You can use bigger size than 256K for disk buffers.
But every installation is different, so you must perform backup and restore tests to find the best value for all buffers. Do not forget to test network buffers sizes.
check this pdf
http://www.symantec.com/connect/sites/default/files/IA%20B47.pdf
08-14-2013 08:33 AM
Use 256K block size for tape as well. You are right about virtual tapes are considered normal tape for Netbackup
NUMBER_DATA_BUFFERS/SIZE_DATA_BUFFERS are in play here.
You can't tell Netbackup to treat a VTL as disk - Netbackup consider VTL as tape and handle it as such. After all Netbackup know it's writing to tape thru device driver (even if tape is emulated by a VTL)
You use the same values for both VTL and physical tapes - but I can recall why you would use different values. Ually bigger scsi block sizes means less system overhead
I did this test many years ago when LTO3 was hot but it still show what buffer tuning can do:
Before tuning: 19MB/sec (default values)
Second tuning attempt: 49MB/sec (using 128K block size, 64 buffers)
Final result: 129MB/sec (using 128K block size and 256 buffers)
08-14-2013 08:39 AM
I'm using 256K for all modern tape devices including VTL. You can use bigger size than 256K for disk buffers.
But every installation is different, so you must perform backup and restore tests to find the best value for all buffers. Do not forget to test network buffers sizes.
check this pdf
http://www.symantec.com/connect/sites/default/files/IA%20B47.pdf
08-14-2013 09:39 AM
Thank you Nicolai and Stefanos, I am keeping the 256K value.
The document Stefanos posted a very good one, thanks.