Our NetApp Nearstore VTL will do the
following when you initiate import from a physical tape:
It will immediately mount the tape and
start importing(depending on available physical drives, it doesn’t
pre-empt the write queue to read anything). The tape is immediately seen by the
media server as soon as importing starts. Data will be read from the physical
tape and laid down to disk inside the VTL.
Then, one of two things will happen.
1: If the VTL has time to read the entire
contents of the data, it will simply lay it down on disk from start to finish,
and unmount the physical tape from the drive, and let the data sit on disk
awaiting restore. When you go to restore, it is very quick. Positioning is
instantaneous, and read speeds are blazing, 120-130MB/s
2: If you decide to start the restore before
the piece of data you’re interested in is read off the tape, the VTL will
stop the import, skip ahead on the physical tape to the file marker requested,
and data is passed directly to the media server without being staged on to the
VTL disk. In this case, the positioning is slower, as it is in fact the
physical tape being manipulated, as well as read speeds, will be whatever is
coming off the physical tape at a given point. The rest of the data on tape
will be read and imported when it is able to do so
All of this is transparent to NetBackup.
The import speed is pretty much whatever
the physical drive is able to give you, it’s data dependent and we’re
seeing approx 70-80 MB/s on LTO-2 tapes, 80-95 MB/s on LTO-3 tapes.
This is how NetApp VTLs work, I cannot
comment on other products.
So, in summary, the time taken to import is
a factor, but somewhat mitigated by the “bypass” operations. Another
complication is of course the need to do this preparation step in the VTL
before NetBackup gets involved.
From: Shyam Hazari
[mailto:shazari AT gmail DOT com]
Sent: Friday, March 07, 2008 12:34
PM
To: Meidal, Knut
Cc:
veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] VTL
& NetBackup Best Practice
Knut,
I am just curious how significant is the time taken to import data to VTL.
-Shyam
On Fri, Mar 7, 2008 at 1:14 PM, Meidal, Knut <kmeidal AT amgen DOT com> wrote:
We converted our environment from Vault to using the
"Direct Tape Copy" feature of our VTLs.
Bad:
- Requires additional
steps to import data to VTL before restore can start