The problem has been brought under control:
I have reduced the maximum chunksize for the holdingdisk to 2000 MB:
datarates of the dumper are now 7000+ kB/s while the taper datarates are
kept at 3000-3500 kB/s. This suggests usage of the holdingdisk.
Also: I more carefully examined the amstatus reports of the failed and now
succeeding backups. The thing that springs to the eye is that the dumper was
waiting 45-60 minutes (out of 4 hrs backup sequence) for the failing
configuration, while this waiting for diskspace now completely disappeared.
(Maybe use all diagnostics all the time!!)
I also double the tapecycle days from 5 to 10 days. The amount of data crept
up to 300 GB. That loads a 5 days cycle on 80 GB tapes to the limit. The net
effect is that the tapes are only written up to 30-40 GB. If the taper
datarates are still too low, the 'gap tracks' will easily fit.
I am again a happy amanda user.
-----Original Message-----
From: Jon LaBadie [mailto:jon AT jgcomp DOT com]
Sent: Wednesday, January 04, 2006 6:11 PM
To: 'amanda-users AT amanda DOT org'
Subject: Re: FW: VXA-V23 taoe difficulties
On Wed, Jan 04, 2006 at 04:13:25AM -0600, Hommersom, Gerrit (G) wrote:
> I've followed with great interest the discussion on this topic as it
> pertains to my backup system
>
> The problems with premature end-of-tape failures persist with big
> DLE's. (order 30-35 GB). The problem gets more severe from 1 failure
> per cycle to daily failures currently. No dumps are left on the
> holding disk.
>
> Closer inspection of the Exabyte FAQ learned that this may occur if
> the datarate to the drive is too low. The drive waits for input while
> writing 'gap tracks' that uses physical space.
>
> I re-examined the amanda logs and saw that for large DLE's the
> datarate for the dumper and taper are the same and in the order of
> 3300 KB/s. VXA2 units write at 6000 KB/s The main raid-5 taperack is
> an external SCSI2 unit. The tape is external SCSI2 too. The holding
> disk is 39 GB on an internal SCSI2 disk.
>
> My questions:
> will amanda use the holding disk for DLE's from on local disk to
> another i.e. will DLE's from the external filsystem use the holding
> disk before taping.
Basically the amanda server, when backing up itself, is backing up a remote
client. It doesn't do anything unique for "local" DLEs vs. "remote" DLEs.
They are all remote.
> I accidentally defined a holdingdisk chunksize of 10 GB on a standard
> (32
> bit) linux system. What would be the effect: direct write to tape ??
No, chunksize is the "maximum" size of any file it will create on the
holding disk. If a DLE is larger than 1 chunk, additional chunks are used.
Where this would create problems is if your OS did not allow files larger
than 2GB (used to be pretty common) and amanda tried to create large chunks.
But that would be a different problem than not using the holding disk.
> What factors may affect the datarate to the tape unit ??
I suspect you have already identified your problem area. Your holding disk
is not being used, either not at all, or at least not for your large DLEs.
I suspect this because of the similarity of taping and dumping rates (how
fast do other large, but not humongous DLEs tape?) and the close match in
size of the DLEs causing problems and the total holding disk space
available.
Amanda decides on a DLE by DLE basis weather to dump to holding disk or
directly to tape. Part of its decision tree is the available space on
holding disk. The amount available is generally lower than the total
because some is "reserve"d for incrementals when the tape drive is
unavailable (see your amanda.conf setting, reserve defaults to 100%
reserved) and by the amount allocated to dumps of other DLEs in progress.
So, for a 30+GB DLE, the space available on a 39GB holding disk could easily
be too small thus causing direct to tape dumping.
So, check if other big DLEs seem to be using the holding disk, check your
reserve parameter and lower it, consider decreasing the size of your DLEs,
increase the size and/or number of hold- ing disks (you can define
multiple). They need not be dedicated. I think I have 4 holding disks
defined. They are just directories on file systems that generally have a
decent amount of free space. I then tell amanda it is free to use all the
space on that FS "except" a certain amount (syntax is something like 'use
-2G') and I define a chunksize reasonable for the amount of space on that
holding disk, big space - large chunks, small space - small chunks.
Let us know how you make out.
--
Jon H. LaBadie jon AT jgcomp DOT com
JG Computing
4455 Province Line Road (609) 252-0159
Princeton, NJ 08540-4322 (609) 683-7220 (fax)
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