[Bacula-users] Questions about slow migration to tape (again)

Hi everyone,

I wrote an e-mail regarding this issue before Christmas and had some good
replies - Thanks to all. However, we were still unable to solve the issue.
We decided to upgrade from 2.0.3 to 2.4.2 (using Ubuntu packages from
Hardy-Backports) to see if we could get it solved.

Unfortunately, it didn't solve the slow migration to tape issue. We had a
suggestion from Ulrich to move spooling to another RAID array, which can't
be done at the moment. So I'm looking at other solutions (if possible).

Here is a recap of our situation:

- Backups are taken from network clients to the Director/SD hard disk
(RAID0, with MySQL on the same array) and then later migrated from disk to
Tape (LTO3 with hardware compression)
- When migrating, it takes hours to write some MB to the tape (i.e. 1h45mins
for 5MB, with a rate of 0.9KB/s)
- I tested the Tape drive with dd and have good throughput, around 135MB/s.


Related to that, I have 2 questions:


Question 1:

When I do a migration to tape, while the first job is migrated, I'm
executing "status storage=Tape" and I see something like the following
output:

--snip--
Device status:
Autochanger "Autochanger" with devices:
   "IBM-ULTRIUM-TD3" (/dev/nst0)
Device "FileStorage" (/backup/bacula) is mounted with:
    Volume:      WeeklyFileVolume-0002
    Pool:        *unknown*
    Media type:  File
    Total Bytes Read=159,528,829,516 Blocks Read=1,360,087
Bytes/block=64,512
    Positioned at File=57 Block=2,323,636,495
Device "IBM-ULTRIUM-TD3" (/dev/nst0) is mounted with:
    Volume:      000014L3
    Pool:        Weekly Tape Pool
    Media type:  LTO-3
    Slot 4 is loaded in drive 0.
    Total Bytes=87,741,932,544 Blocks=0 Bytes/block=64,512
    Positioned at File=0 Block=1
--snip--

>>From "FileStorage",  the "Total Bytes Read" always go over the "Total Bytes"
in the "IBM-ULTRIUM-TD3" section. Why is that? Isn't supposed to be the same
total in both section? It seems like the following is happening:

1. Read and write to tape (I've done the math, and write speed is around 3
GB/min there?!)
2. When job writing is done, the FileStorage read continues (I think this is
where we have a problem)
3. When reading is done, "Migration OK" e-mail report is sent, showing poor
stats about duration and speed rate.

Can someone explain that to me?


Question 2:

Would spooling help in our situation? Or it is just a waste of Disk I/O
since it is a migration from local hard disk to Tape Drive and not backup
from a network client directly to Tape?


Thanks for you help, very appreciated!


J-P




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