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Compression during cloning
I have 7.6.2 version of EMC Networker. two storage nodes besides networker server, to these storage nodes MSL 4048 library with 2 drives is connected thru SAN
I have configured Clones, the cloning occurs from one tape to another. I noticed that my backup tapes able to handle almost 2000 GB of data, but when I cloned the same data the cloning tapes have only 1500 GB and 500 GB. so from my point of view there is no compression on tape.
Why on earth this is happening. I tried switching the drives in cloning process - the result is the same. Now I am implementing encryption, but afraid that after cloning there will be no encryption at all.
Neodarek
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December 26th, 2011 01:00
The original backup compressed by drive itself, so it's hardware compression, not software. So the LTO5 tape can have in my case 1800-2000 GB of data. But when I clone these compressed tapes, the resulting tapes do not have any more than uncompressed capacity of LTO5 tape.
For example, asume I have one tape with backuped data, and the size of data on this tape is 2050 GB. Then I clone this tape and in end of cloning I have 2 tape - one with 1500 GB data and the other with 550 GB of data. So what in backup process was stored on one tape, after cloning proccess stored on 2 tapes.
I do not understand why this is happening at all
DavidHampson-rY
294 Posts
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December 26th, 2011 01:00
If your original backup has been compressed it will not compress further by cloning it. You will see similar if your backup data is already in a compressed form (things like .zip, .mp3, .jpg, .tar etc).
coganb
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December 29th, 2011 06:00
Is the first of the two tapes that is the target of the cloning marked full? Have you got parallel nsrclone commands running or is there just one stream from automatic cloning? Is the amount of data you get on the first target tape and the second consistently the same?
-Bobby
ble1
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January 10th, 2012 07:00
Are you reading from the same host and writing to the same host? In case of different hosts, aka cloning via LAN, check if you run same drivers (for example, maybe depending on OS, I know I had to use IBM drive handles to enable HW compression as IBM LTO didn't care about native compression handle by HPUX). Further, is this the same library? And last, compression can be set on drive level (HW) - connecting to library and checking this up would be something to do too.