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Expiring images currently on tape

Hello

I have an issue, but most, i think is a lack of understanding how the expiring of images on tapes really works.

I think it would be better explained with an example: When i browse in the catalog for images on certain tapes and realize that i do not care anymore for those images (and want to recover the space in tape that those images take) i right-click all the images and select "Expire". Here is the problem, the images are expired but when i look at the console (Media and Device Management>>Media>>Volume Pools>>Pool1) i don't see that i recover that space on tape those images were occupying.

That procedure usually works for me when we are talking about images on disk. The image is actually expired (deleted from disk) and, of course, i recover the space on disk i was looking for.

I actually think that the images expiration is quite trickery sometimes. I usually run into situations when the retention I previously defined in my policy is not respected (if a set up a retention of 1 week, after one week the images are still there. Why does the tool require my intervention to manually expire the image?). I know that this is a different question from my main topic (Howto recover the space on tape a image was taking after its expiration) but still worth to mention

Any help will be well received!

1 Solution

Accepted Solutions
Accepted Solution!

As you have learned, backups

As you have learned, backups on tape are different than those on disk. 

When you expire a backup on tape, all you are doing is telling the NetBackup catalog to remove the index information it would use to locate the individual files in the backup image.  The tape is not mounted when data expires, and no data is erased.  Once ALL backup images on that tape have expired, either automatically or manually, the next daily Image Cleanup job (check your activity monitor to see when this runs) will determine if the images on the media have all been expired and the tape will be reassigned back to your SCRATCH pool so that it can be used again.  Again, the tape is not going to be mounted, nothing is physcially erased from it.  The tape will be overwritten the next time NetBackup needs a scratch tape and happens to select this same media ID.

On the other hand, when data on disk is expired, the data is (usually) physically deleted at the time you expire the image.  If you are using a deduplication backup appliance or MSDP/Puredisk disk storage unit, there will also have to be a separate cleanup/data recalamation job, usually running outside of NetBackup so you won't see it in the Activity Monitor, that will recover the used space on the device.

You should never be expiring images on tapes manually unless you have specifically architected your NetBackup system in such a manner and have a very, very good reason to do so.  NetBackup has a  feature, found in the master server's properties under "Media", that is called "Allow multiple retentions per media"; this is unchecked by default.  If this is still unchecked, than NetBackup will group backup images with the same retention period onto the same tape.  It will append future backups with the same retention period to that same tape for days and days, unless you do something to suspend/freeze/eject the tape.  This will mean that the backup image data at the beginning of the tape might expire, say, a week from today, but it may take 3, 4, 5 days or more before all the data expires.  During that time, you cannot write data to that tape again.  Once all the data expires, the tape will move back to the scratch pool and can be resued. 

This is the most efficient use of tape in large environments where data is kept for long periods of time, like infinity.  You will send fewer tapes offsite if all of the data that needs to be kept for a long time is stored on as few tapes as possible.

If you check the "Allow multiple retentions per media" option, you may end up with data on the tape that will expire next week, some that may expire in a month, etc., and some that may be kept forever, in which case only some of the space will actually be used and your tape could be sent offsite forever.

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2 Replies
Accepted Solution!

As you have learned, backups

As you have learned, backups on tape are different than those on disk. 

When you expire a backup on tape, all you are doing is telling the NetBackup catalog to remove the index information it would use to locate the individual files in the backup image.  The tape is not mounted when data expires, and no data is erased.  Once ALL backup images on that tape have expired, either automatically or manually, the next daily Image Cleanup job (check your activity monitor to see when this runs) will determine if the images on the media have all been expired and the tape will be reassigned back to your SCRATCH pool so that it can be used again.  Again, the tape is not going to be mounted, nothing is physcially erased from it.  The tape will be overwritten the next time NetBackup needs a scratch tape and happens to select this same media ID.

On the other hand, when data on disk is expired, the data is (usually) physically deleted at the time you expire the image.  If you are using a deduplication backup appliance or MSDP/Puredisk disk storage unit, there will also have to be a separate cleanup/data recalamation job, usually running outside of NetBackup so you won't see it in the Activity Monitor, that will recover the used space on the device.

You should never be expiring images on tapes manually unless you have specifically architected your NetBackup system in such a manner and have a very, very good reason to do so.  NetBackup has a  feature, found in the master server's properties under "Media", that is called "Allow multiple retentions per media"; this is unchecked by default.  If this is still unchecked, than NetBackup will group backup images with the same retention period onto the same tape.  It will append future backups with the same retention period to that same tape for days and days, unless you do something to suspend/freeze/eject the tape.  This will mean that the backup image data at the beginning of the tape might expire, say, a week from today, but it may take 3, 4, 5 days or more before all the data expires.  During that time, you cannot write data to that tape again.  Once all the data expires, the tape will move back to the scratch pool and can be resued. 

This is the most efficient use of tape in large environments where data is kept for long periods of time, like infinity.  You will send fewer tapes offsite if all of the data that needs to be kept for a long time is stored on as few tapes as possible.

If you check the "Allow multiple retentions per media" option, you may end up with data on the tape that will expire next week, some that may expire in a month, etc., and some that may be kept forever, in which case only some of the space will actually be used and your tape could be sent offsite forever.

View solution in original post

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