Bacula-users

Re: [Bacula-users] slow despool to tape speed?

2012-04-13 06:55:12
Subject: Re: [Bacula-users] slow despool to tape speed?
From: Martin Simmons <martin AT lispworks DOT com>
To: bacula-users AT lists.sourceforge DOT net
Date: Fri, 13 Apr 2012 11:53:29 +0100
>>>>> On Fri, 13 Apr 2012 09:13:31 +0000, Steve Costaras said:
> 
> Yes, it seems that bacula 5.2.6 has a problem or is not accepting the change 
> for larger Maximum Block Size:
> 
> ------
> Device status:
> Device "FileStorage" (/tmp) is not open.
> Device "LTO4" (/dev/nst0) is mounted with:
>     Volume:      FA0060
>     Pool:        BackupSetFA
>     Media type:  LTO4
>     Total Bytes=13,974,653,952 Blocks=216,620 Bytes/block=64,512
>     Positioned at File=1 Block=50,181
> ====
> 
> It's falling through down to 64512 when I have anything set larger than 
> 2097152 for maximum block size.

Yes, but it looks like this fails to report the error on startup:

   if (dev->max_block_size > 4096000) {
      Jmsg3(jcr, M_ERROR, 0, _("Block size %u on device %s is too large, using 
default %u\n"),
         dev->max_block_size, dev->print_name(), DEFAULT_BLOCK_SIZE);
      dev->max_block_size = 0;
   }


> WITH 2097152 as maximum block size I'm getting:
> 
> ---
> Device status:
> Device "FileStorage" (/tmp) is not open.
> Device "LTO4" (/dev/nst0) is mounted with:
>     Volume:      FA0060
>     Pool:        BackupSetFA
>     Media type:  LTO4
>     Total Bytes=223,244,193,792 Blocks=106,452 Bytes/block=2,097,134
>     Positioned at File=20 Block=4,070
> ====
> --
> 
> which is smaller than what I'm setting by ?18 bytes?  I don't get that at all.

It is a maximum, so you can't expect every block to be that size.

__Martin

> 
> 
> Looks like there may also be a file system prefetch caching issue on top of 
> this as even with the above larger block size I'm still only getting 50MB/s  
> (this is now on a raid-0 of 16 2TB drives).
> 
> 
> >From: Steven Ellis
> >
> >>On 4/12/2012 5:55 PM, Steve Costaras wrote:
> >> My bacula-sd.conf is:
> >>
> >> ---
> >> Device {
> >>    Name = LTO4
> >>    Changer Device = /dev/sg87
> >>    Alert Command = "sh -c 'smartctl -H -l error %c'"
> >>    AlwaysOpen = yes;
> >>    Archive Device = /dev/nst0
> >>    AutomaticMount = yes;
> >>    Maximum Block Size = 4194304
> >>    Maximum File Size = 10G
> >>    Maximum Job Spool Size = 800G
> >>    Maximum Network Buffer Size = 262144
> >>    Maximum Spool Size = 12800G
> >>    LabelMedia = No
> >>    Media Type = LTO4
> >>    RandomAccess = no;
> >>    RemovableMedia = yes;
> >>    Spool Directory = /scratchdir/spool0
> >> }
> >> -------
> >That does seem to be what it indicates to me (but I'm still running 
> >5.0.3, so YRMV), however, I found that my end-of-media messages 
> >typically look like this:
> >
> >2012-03-04 11:30:20 sweety-sd End of Volume "MO0038L3" at 92:1171 on 
> >device "LTO3" (/dev/nst0). Write of 262144 bytes got -1.
> >2012-03-04 11:30:24 sweety-sd Re-read of last block succeeded.
> >
> >And my block size is set to 262144 (aka 256K), whereas the default block 
> >size is 64512, (aka 63K)--since you are seeing a (presumably full, but 
> >maybe not) block that fills the media being only 63K long, it at least 
> >seems that somehow your configured block size is not being observed.
> >
> >Another point towards that end, even assuming that the current file on 
> >the tape was nearly complete (i.e. 10GByte), then it isn't possible that 
> >you were at block 91229 (which the log message indicates you were) with 
> >a block size anywhere near 4MB (in fact, 10GiB/91229 = ~115KiB). It 
> >looks like the largest possible average block size you saw in the last 
> >file was about 115Kbytes (and if the last file was a bit less than half 
> >complete, this would be consistent with an average block size of ~63K).  
> >I don't fully understand bacula's blocking mechanism, but this seems 
> >unusual to me (given your configured file size of 10G and maximum block 
> >size of 4M).
> >
> >-se
>

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