Jump to content

Compression question


Recommended Posts

Quick question:

 

I have my backup server (Mac Mini) attached to a LTO 5 tape drive and my backup script ejects the tape and wants another tape after only backing up 1.8TB of data. I have Allow Hardware Compression enabled in the backup script but yet still stops backing up at 1.8TB. Any ideas on why its not writing the full 2.9TB the tape can hold?

Link to comment
Share on other sites

Tape capacities can only be estimated until the tape is actually full. The native capacity of an LTO-5 tape is 1.5 TB. The advertised capacity of 2.9 or 3 TB assumes 50% compression. If the files you're backing up can't be compressed that much, you will get less data on the tape. Also, backing up lots of small files will waste some tape, as the tape drive is less efficient when it has to shuttle back and forth between writing and reading.

 

Retrospect will write to the tape until the drive reports that the tape is full. 1.8 TB is not an unreasonable total to expect when backing up relatively uncompressible files.

 

If Retrospect asks for a new tape after backing up an unexpectedly small amount of data (i.e., less than the native capacity), that can indicate that the tape drive has encountered a problem writing to the tape.

Link to comment
Share on other sites

It ejects the tape and wants another one for only 62GBs, this has happened on a used and brand new tape.

 

I'm trying to avoid using the software compression, if this is truly all the tape will hold compressed by hardware then this is my only other option aside upgrading my tape drive to LTO 6

Link to comment
Share on other sites

It ejects the tape and wants another one for only 62GBs, this has happened on a used and brand new tape.

That suggests a problem with your tape drive, or that something went wrong during the most recent backup to the media set in question. Do you see any errors in the operations log?

 

 

I'm trying to avoid using the software compression, if this is truly all the tape will hold compressed by hardware then this is my only other option aside upgrading my tape drive to LTO 6

All LTO drives that I am aware of have hardware compression. Software compression is disabled when backing up to a device that supports hardware compression.

Link to comment
Share on other sites

No, there are no errors in the log.

 Normal backup using Monthly Full at 2/29/16, 8:00:00 PM (Activity Thread 1)
    To Backup Set M2T Feb 16...
    2/29/16 8:00:00 PM: Recycle backup: The Backup Set was reset
    -  2/29/16 8:00:00 PM: Copying Backup 2 Disk
    Using Instant Scan
    2/29/16 8:00:01 PM: Found: 3187 files, 5 folders, 1.8 TB
    2/29/16 8:00:01 PM: Finished matching
    2/29/16 8:00:01 PM: Copying: 3187 files (1.8 TB) and 0 hard links
    3/1/16 8:48:39 AM: Execution stopped by operator
    Remaining: 112 files, 62.6 GB
    Completed: 3,075 files, 1.8 TB
    Performance: 7,078 MB/minute
    Duration: 12:48:39 (08:29:07 idle/loading/preparing)

This is a

1. brand new backup script

2. brand new media set 

3. brand new tape

4. drive is only about a year old and has never failed me before.

Link to comment
Share on other sites


Normal backup using Monthly Full at 2/29/16, 8:00:00 PM (Activity Thread 1)
To Backup Set M2T Feb 16...
2/29/16 8:00:00 PM: Recycle backup: The Backup Set was reset
- 2/29/16 8:00:00 PM: Copying Backup 2 Disk
Using Instant Scan
2/29/16 8:00:01 PM: Found: 3187 files, 5 folders, 1.8 TB
2/29/16 8:00:01 PM: Finished matching
2/29/16 8:00:01 PM: Copying: 3187 files (1.8 TB) and 0 hard links
3/1/16 8:48:39 AM: Execution stopped by operator
Remaining: 112 files, 62.6 GB
Completed: 3,075 files, 1.8 TB
Performance: 7,078 MB/minute
Duration: 12:48:39 (08:29:07 idle/loading/preparing)

I misunderstood your second question. I thought you were saying that Retrospect was asking for a third tape after backing up only 62 GB to tape #2. 

 

Backing up "only" 1.8 TB to an LTO-5 tape is a pretty normal result. If you need more capacity per tape, you will need to move to LTO-6 or LTO-7. If you simply need more capacity per backup and want it to be able to complete without user intervention, you might want to consider a tape library.

 

Link to comment
Share on other sites

If I un-enable Allow Hardware Compression in the media set would the software compression work if I set it in the script?

 

I don't know of a way to disable hardware compression for an existing media set. You need to deselect that option when the media set is first created.

 

Hardware compression is certainly faster and probably also more efficient than Retrospect's software compression. I wouldn't recommend going that route, but you could experiment with a new tape media set and see if you're happy with the result.

 

We use LTO-5 tapes, and typically get between 1.6 TB and 2.3 TB per tape, depending on what kinds of files are being backed up.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...