Hello,
It generally helps to read the manual in cases like this. Here is a short
except from the manual that should pretty much explain it:
Bacula's preferred method of working with tape drives (sequential devices) is
to run in variable block mode, and this is what is set by default. You should
first ensure that your tape drive is set for variable block mode (see below).
If your tape drive is in fixed block mode and you have told Bacula to use
different fixed block sizes or variable block sizes (default), you will get
errors when Bacula attempts to forward space to the correct block (the kernel
driver's idea of tape blocks will not correspond to Bacula's).
All modern tape drives support variable tape blocks, but some older drives
(in particular the QIC drives) as well as the ATAPI ide-scsi driver run only
in fixed block mode. The Travan tape drives also apparently must run in fixed
block mode (to be confirmed).
Even in variable block mode, with the exception of the first record on the
second or subsequent volume of a multi-volume backup, Bacula will write
blocks of a fixed size. However, in reading a tape, Bacula will assume that
for each read request, exactly one block from the tape will be transferred.
This the most common way that tape drives work and is well supported by
Bacula.
Drives that run in fixed block mode can cause serious problems for Bacula if
the drive's block size does not correspond exactly to Bacula's block size. In
fixed block size mode, drivers may transmit a partial block or multiple
blocks for a single read request. From Bacula's point of view, this destroys
the concept of tape blocks. It is much better to run in variable block mode,
and almost all modern drives (the OnStream is an exception) run in variable
block mode. In order for Bacula to run in fixed block mode, you must include
the following records in the Storage daemon's Device resource definition:
Minimum Block Size = nnn
Maximum Block Size = nnn
where nnn must be the same for both records and must be identical to the
driver's fixed block size.
We recommend that you avoid this configuration if at all possible by using
variable block sizes.
If you must run with fixed size blocks, make sure they are not 512 bytes.
This is too small and the overhead that Bacula has with each record will
become excessive. If at all possible set any fixed block size to something
like 64,512 bytes or possibly 32,768 if 64,512 is too large for your drive.
See below for the details on checking and setting the default drive block
size.
To recover files from tapes written in fixed block mode, see below.
On Friday 24 November 2006 21:06, Peter Crighton wrote:
> I now have found btape so I set my tape testing on fill this morning.
>
> After 12 hours it's only managed 3GB. It is reporting about 70kb/s,
> which is consistent with the rate it's reporting.
>
> With other programs (Windows 98/Veritas backup and Linux/Amanda) it
> can fill a 10GB tape in that time (it's spec is 60MB/min and as I
> recall but didn't note Amanda was not far off - from memory I think it
> was a about 40MB/min).
>
> I have had to set 512 byte blocks (it didn't work with variable size
> and mt reports that it has 512 byte blocks). Others have also reported
> this requirement. The drive is on an IDE cable shared with the CDROM
> (not in use) so it should have full access to the IDE port.
>
> With other programs when writing data the tape whirrs continuously in
> one direction. With btape it is winding one way then silent the
> rewinding then going forward (that's what it sounds like anyway). That
> will clearly hit the performance if it doesn't write continuously.
>
> The drive is a Travan 20 (10GB native, 20GB compressed) Seagate
> STT220000A.
>
> Clearly the performance is much reduced from what the drive is capable
> of. Has anyone suggestions (ideally first hand experience of this or a
> very similar model, e.g the STT28000A 8GB/4GB version) that could
> help?
>
> The drive may be a few years old, but it's capacity and speed (when
> it's going at it's flat out speed) suits my requirements, plus I have
> a second drive in another machine which gives me some redundancy in
> the event of a failure).
>
> This is the definition that I added to bacula-sd.conf:
>
> Device {
> Name = Travan
> Description = "Travan 10/20GB"
> Media Type = TR-5
> Archive Device = /dev/nst0
> AutomaticMount = yes;
> AlwaysOpen = yes
> Offline On Unmount = no
> Fast Forward Space File = no
> Hardware End of Medium = no
> Minimum Block Size = 512
> Maximum Block Size = 512
> }
> --
>
> Peter Crighton
>
> -------------------------------------------------------------------------
> Take Surveys. Earn Cash. Influence the Future of IT
> Join SourceForge.net's Techsay panel and you'll get the chance to share your
> opinions on IT & business topics through brief surveys - and earn cash
> http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
> _______________________________________________
> Bacula-users mailing list
> Bacula-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/bacula-users
>
-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys - and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
_______________________________________________
Bacula-users mailing list
Bacula-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/bacula-users
