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ggirao

Read and Write Speed

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I'm getting on optimal conditions speeds about 2.6-3 GB/m on LTO4 tapes. I Will need to restore some stuff and time is critical, need to know if there is any comparision on read speeds.

 

TY

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The speed while actually reading is the same.

However, the wanted files are probably spread over the tape (or several tapes) so it will be a lot of positioning to find the right place (on the right tape).

This is due to file de-duplication, also called Single-instance storage: http://en.wikipedia.org/wiki/Single-instance_storage

If an identical file exists on many computers, it is backed up once. It may reside on another computer than the one you are restoring.

 

For fastest restores (and also for faster backups) use disk-to-disk-to-tape. Buy a large disk, run backups from the clients to a disk media set. Then run a transfer snapshots script from the disk media set to the tape media set.

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We use disk-to-disk-to-tape! But I have seen speeds of reading from tape writing do disk about 5GB/m today. I have never passed 3GB on reverse way.

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However, the wanted files are probably spread over the tape (or several tapes) so it will be a lot of positioning to find the right place (on the right tape).

This is due to file de-duplication, also called Single-instance storage: http://en.wikipedia....nstance_storage

If an identical file exists on many computers, it is backed up once. It may reside on another computer than the one you are restoring.

 

You mentioned this and today I made a restore that didn't match source vs destination sizes. Can be this?

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Yes, I understand that it's about backup/restore.

 

You wrote: "I made a restore that didn't match source vs destination sizes."

Where do you see the "source" size and where do you see the "destination" size? What are the sizes?

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well:

 

I Made a 1rst backup to a media set, saw the size under the log. Get info from the folder under de OS, and they just doesn't match. When I did a restore the size was the size of the stuff backed up.

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First of all, files on a disk is allocated in blocks of 4kB. So a 1 byte file takes up 4kB. A 4001 byte file takes up 8kB.

You must use the exact numbers in the Finder:

post-8868-0-58959900-1361261836_thumb.png

 

Second, you may have a filter/selector that excludes files that resides in the folder.

 

Third, some files may have been backed up in an earlier backup, so they are not copied again.

 

Fourth, if that is the only backup to that media set, you may still have duplicate files. Duplicates are backed up only once.

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