Sweet! I did not know that. I'll take that ANY day of the week. Thanks
Edward & John for the responses.
On Wed, Feb 8, 2012 at 2:58 PM, Edward M. Markowski <e...@edmarkowski.com>wrote:
>
> I also used to think that the upper number in the tape raiting was a hard
> limit, it is not.
>
> You just happen to have data in your file system that is HIGHLY
> compressable, congrats.
>
> On Wed, 8 Feb 2012, Josh Nielsen wrote:
>
> Hello,
>>
>> I am relatively new to tape backups in general and I have recently become
>> accustomed to using bacula, and I have a quick question about compression
>> ratios/storage capacity on LTO tapes. I have an IBM 24-tape library with
>> Sony Ultrium LTO-4 tapes (Rated: 800GB/1,600GB compressed). I recently set
>> a job for a
>> full backup of one of our servers that has a little over 3TB of disk
>> capacity. A du -h of that server yields:
>>
>> Filesystem Size Used Avail Use% Mounted on
>> /dev/mapper/VolGroup00-**LogVol00
>> 3.3T 2.2T 983G 70% /
>>
>> My question relates to this: from a fresh install of bacula (5.0.3) I
>> created a pool for monthly backups and ran a full backup of that server
>> above. All the
>> tapes were marked empty and the backup started by picking a tape from the
>> designated pool and backed up successfully to it, but I fully expected it
>> to span
>> _two_ tapes with 1.6TB as the supposed maximum "rated" compression
>> capacity for LTO-4 tapes. However it fit _all of it_ onto a single tape.
>> Here is an excerpt
>> from the job output:
>>
>> Storage: "IBM_Autochanger" (From Job resource)
>> Scheduled time: 07-Feb-2012 10:26:00
>> Start time: 07-Feb-2012 10:26:02
>> End time: 07-Feb-2012 21:08:39
>> Elapsed time: 10 hours 42 mins 37 secs
>> Priority: 10
>> FD Files Written: 458,656
>> SD Files Written: 458,656
>> FD Bytes Written: 2,362,329,795,537 (2.362 TB)
>> SD Bytes Written: 2,362,399,227,266 (2.362 TB)
>> Rate: 61268.5 KB/s
>> Software Compression: None
>> VSS: no
>> Encryption: no
>> Accurate: no
>> Volume name(s): ML1038L4
>> Volume Session Id: 1
>> Volume Session Time: 1328631897
>> Last Volume Bytes: 2,364,166,103,040 (2.364 TB)
>>
>> And 'list media' showed the pool as follows:
>>
>> Pool: Monthly
>> +---------+------------+------**-----+---------+--------------**
>> -----+----------+-------------**-+---------+------+-----------**
>> +-----------+-----------------**----+
>> | MediaId | VolumeName | VolStatus | Enabled | VolBytes | VolFiles |
>> VolRetention | Recycle | Slot | InChanger | MediaType | LastWritten |
>> +---------+------------+------**-----+---------+--------------**
>> -----+----------+-------------**-+---------+------+-----------**
>> +-----------+-----------------**----+
>> | 19 | ML1037L4 | Append | 1 | 64,512 | 0 |
>> 31,536,000 | 1 | 19 | 1 | LTO-4 | 0000-00-00
>> 00:00:00 |
>> | 20 | ML1047L4 | Append | 1 | 64,512 | 0 |
>> 31,536,000 | 1 | 20 | 1 | LTO-4 | 0000-00-00
>> 00:00:00 |
>> | 21 | ML1044L4 | Append | 1 | 64,512 | 0 |
>> 31,536,000 | 1 | 21 | 1 | LTO-4 | 0000-00-00
>> 00:00:00 |
>> | 22 | ML1041L4 | Append | 1 | 64,512 | 0 |
>> 31,536,000 | 1 | 22 | 1 | LTO-4 | 0000-00-00
>> 00:00:00 |
>> | 23 | ML1038L4 | Append | 1 | 2,364,166,103,040 | 2,365 |
>> 31,536,000 | 1 | 23 | 1 | LTO-4 | 2012-02-07 21:08:17 |
>> +---------+------------+------**-----+---------+--------------**
>> -----+----------+-------------**-+---------+------+-----------**
>> +-----------+-----------------**----+
>>
>> I actually calculated 2,364,166,103,040 bytes to be 2.15 TB, but either
>> way this is much higher than the rated 1.6TB with the (theoretically)
>> maximum
>> compression, as I understand it. Not until I ran another relatively tiny
>> backup afterward (around 90GB) of something else did it fill the first tape
>> and start
>> to write the remaining 80GB or so onto a second tape. The job output
>> above says there was no software compression being used, and unless it is a
>> default I have
>> done nothing to enable (or disable) tape compression on the IBM Library
>> itself.
>>
>> Has anyone heard of getting more capacity out of an LTO-4 tape than it is
>> rated for? Or are the byte amounts inflated, possibly, by artificially
>> counting
>> skipped-over file systems? I got several messages like "/boot is a
>> different filesystem. Will not descend from / into /boot", but you would
>> think that it
>> wouldn't count those in the overall storage amount. I essentially just
>> want to know if these figures are real, and if I'm just getting an awesome
>> compression
>> ratio, or if something else is going on.
>>
>> Thanks!
>> Josh
>>
>>
>>
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