Why Verify speed is 10 times faster then write speed on LTO8 backing up ESXi?

[shaptala]

We experiance very slow write speed when backing up from ESXi hosts (about 2500 MB/m). But when it comes to verify the speed jumps to 20000 MB/m. This is not a problem with write head of LTO8 tape drive, because if I try to write big file on LTO8 drive from local BackupExec server - the speed is 10000 MB/m. Why verify speed of ESXi hosts differ so much from write speed?

[Gurvinder · Accepted solution]

when the backup is done, data is fetched from vmware esx ( in this case ) over the network (nbd) or SAN and then fed to the tape. You can try the steps in this technote to see if the backup rate can be improved ( if there is a scope for improvment ) https://www.veritas.com/support/en_US/article.100026847
For the verify , the storage system records the CRC of the media where the data is being written and in the end when BE starts the verify phase, it is just matching or checking the CRC on the media w.r.t what was saved during the write by storage system and hence it is really fast. Verify is normally faster than Backup/Write.

[shaptala]

Can you answer 1 more question? Regarding improving speed of ESXi backup. If I configure direct access to SAN - will the data goes still via BackupExec server or it will go directly to tape? I am just trying to remove bottlneck.

[Gurvinder]

via BE.