My recollection is that during duplication
from VTL to tape , it uses the mpx originally set in the policy unless it is
throttled down by the vault policy but you can’t increase it. The MPX is
what is so interesting to examine in truss because I observed that any
multiplexing will impact the duplication speed.
This is impact more pronounced though when
you are mixing slow and fast clients together because the fragments are not
spread out evenly on the virtual tape and bptm has to rewind the virtual tape
and reread, causing a delay to physical library which is torture on the
physical tape drive
Then I observed
that a higher MPX led to a slight improvement in duplication speed. I would use
24-32
However there are
other tradeoffs. In the end we decided to not use VTL for network client backups
for the new master server environment model.
A problem with
VTLis that a slow client backup will hold onto the vritual media preventing me
from using it for duplication. This impacts the RPO of other clients backups. DSU
does not have that issue.
We use 64TB EVA
file systems per network media server which give pretty even performance and we
use vxfs.
One outstanding
issue with file systems that you don’t have with VTL is fragmentation
Another benefit of VTL is that I have a media server dedicated to writing the
backups and another media server dedicated to duplicating backups.
.
__________________________________________
Jonathan Marianu (mah ree ah' nu)
AT&T Storage Planning and Design Architect
(360) 597-6896
Work Hours 0800-1800 PST M-F
Manager: David Anderson
(314) 340-9296