The statement "DSA backups are better" is not entirely true. I've run into
issues with NetApp using DSA, when we tried to do DAR and DDAR restores,
we found that there are some architectural limitations on the NetApp side
when talking to any remove NDMP Tape Server. Specifically:
1. 100-200ms delay between requests. This can be disabled via a ndmpd
argument.
2. Maximum of 1.3MB per transfer, with 10 transfers per second. When small
sized data is being restored, the size of each transfer is much smaller.
This should not be an issue when doing non-DSA restores, but of course
you'll have to read through the entire saveset until you get to your data,
so it could potentially be slower overall. (That is where the "keep NDMP
backup sizes to a reasonable size" comes in to play)
--Dave
Date: Tue, 27 Mar 2012 06:51:50 -0700
From: bingo <networker-forum AT BACKUPCENTRAL DOT COM>
Subject: D2D2T information layout
It depends.
Only for NetWorker backups NW will use its own format. In fact, it is the
same no matter which media is used for backups. That's why one can use the
same mechanisms in both places (tools like 'scanner' work the same way).
There is no more change when moving it
For NDMP backups, it is different as only NDMP writes the data - NW will,
actually it can't, embed meta data. That's why you should sent NDMP data
to separate tape pools. You also need NDMP specific save/recover/clone
commands. Additionally, NDMP only supports local backup to tape (unless
you add a NDMP tape driver on a storage node or use another NDMP filer of
the same manufacturer).
However, since NW 7.2? you may use NW's embeed Data Storage Agent (DSA)
which 'wraps' the NDMP data into 'normal' NW backup data packages so that
the first rule will apply again. Assuming your network being fast enough,
DSA backups are the better and more flexible alternative.
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