3592 JC tape, unexpected low capacity

Lars-Owe

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PREDATAR Control23

Much of our data is already compressed, so I don't expect much from hardware compression, but why is there significantly less data than the nominal capacity on some of our tapes? Here's one with only 2 out of 4TB:

>q vol c00109 f=d

Volume Name: C00109
Storage Pool Name: BACKUP3584_2
Device Class Name: 3584_2CLASS
Estimated Capacity: 2.0 T
Scaled Capacity Applied: 100
Pct Util: 99.7
Volume Status: Full
Access: Read/Write
Pct. Reclaimable Space: 0.3
Scratch Volume?: Yes
In Error State?: No
Number of Writable Sides: 1
Number of Times Mounted: 3
Write Pass Number: 1
Approx. Date Last Written: 03/18/2015 16:36:34
Approx. Date Last Read: 03/17/2015 04:36:18
Date Became Pending:
Number of Write Errors: 0
Number of Read Errors: 0
Volume Location:
Volume is MVS Lanfree Capable : No
Last Update by (administrator):
Last Update Date/Time: 03/17/2015 04:17:17
Begin Reclaim Period:
End Reclaim Period:
Drive Encryption Key Manager: None
Logical Block Protected: No

Generally speaking our LTO-5 tapes are the most disappointing.
 
PREDATAR Control23

Are you using TS1140 drives?

Advertised maximum capacity is 4TB on TS1140 with hardware compression. Since your data is compressed, this capacity of 2 TB is nominal.
 
Last edited:
PREDATAR Control23

IBM:s data sheet for the TS1140 reads:

Native capacity (uncompressed) 4 TB (using JC/JY media), 1.6 TB (using JB/JX media), or 500 GB (using JK media)

So I guess we'll have to find another explanation.
 
PREDATAR Control23

I
IBM:s data sheet for the TS1140 reads:

Native capacity (uncompressed) 4 TB (using JC/JY media), 1.6 TB (using JB/JX media), or 500 GB (using JK media)

So I guess we'll have to find another explanation.

I have written it wrong. It should have read 4 TB without compression.

Again, if your data is compressed, you would see varied capacity on the tape. This is due to how data is handled - writing/reading on the tape for optimum performance and reliability.
 
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