> >I have always wondered .. why does amanda pipe ufsdump output to
> ufsrestore
> >before sending it to the tape device?
>
> It's collecting the index data.
John, thanks for clarifying...
> >If amanda is dumping direct to tape (file systems that are
> bigger than the
> >holding disk), I'm lucky if i get 1mb/second.
> >
> >If it's going from the holding disk to tape, I get 3mb/second,
> as expected.
>
> But you're comparing apples and oranges. As you've noted, going from
> disk to tape on the same machine gets 3 MBytes/s whether you are using
> ufsdump or Amanda is using taper to copy a holding disk image.
>
> But that's not what happens when Amanda is dumping a client direct to
> tape. The data has to go across the network (even if it's all on the
> local machine it still goes through the kernel network stack). And,
> probably even more important, Amanda does compression when dumping,
> not when writing to tape.
>
> So a dump to holding disk would be "slow" but the corresponding holding
> disk to tape operation would be "fast". But a direct to tape backup
> would pay the penalty and show the speed loss due to compression even
> though the tape I/O portion is going as fast as it is given data.
I should have mentioned, we have several ~10Gb file systems (on the same
system as the tape drive, Amanda server), and none of these are dumped with
compression (for speed reasons).
> You didn't mention what kind of dump rates Amanda reports. Those should
> more or less match your direct to tape numbers for large enough images
> to get a good sample and with similar clients.
The dump rates reported by Amanda are around 1.0-1.5mb/second (without
compression). A direct ufsdump to tape without Amanda on the same file
systems run at 3mb/second (which is the fastest that the tape drive can
accept the data).
Given the complexity of the Amanda sendbackup process this doesn't exactly
surprise me, but I wondered if I could do anything to speed things up.
The system is a little underpowered and perhaps when we get our much needed
upgrade (a nice new dual cpu E220R), things will improve...
g.
