The answer here is pretty simple actually. 

Sdlt320 tapes all store exactly 160gb after compression. The 320gb figure 
quoted is based on an average compression ratio of 2:1. 

Sdlt hardware compression is usually about 2:1 but it can however result in 
'negative' compression if the data you send to the drive is already compressed. 
So when you see tapes storing between about 120gb or more there is likely 
nothing wrong with your tapes. 

Bad tapes show up with write errors in the daemon.log and get marked full as 
soon as an error is seen. However most of the time the errors are caused by 
dirty drive heads and it doesn't hurt to let the tapes get recycled and see if 
the write errors persist. I keep a log of write errors separately and if a tape 
catches my eye as being full but with only 1 or 2 gig I look for its history. 

I would advise you to replace your sdlt drives. This technology is getting too 
old now. 

LTO3 or 4 is in my experience so much better than sdlt and due to volume sales 
the tapes are better value for money by far. 


----- Original Message -----
From: EMC NetWorker discussion <NETWORKER AT LISTSERV.TEMPLE DOT EDU>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU <NETWORKER AT LISTSERV.TEMPLE DOT EDU>
Sent: Tue Aug 05 19:39:34 2008
Subject: [Networker] Quality of the tapes

Hi everyone,

I am basically new to networker. But i would like to ask a question about the 
quality of the data in the tapes or the tapes itself.

The tapes what I am using is HP Super DLT Tapes with capacity 320 GB. I was 
actually going through the inventory and i found out that for some tapes the 
volume written was around 120- 130  GB where as for several other tapes it 
varied between 200-400 GB. What I want to ask is that, I think there are 2 
types of data being written , i.e. compressed as well as uncompressed. So is 
the tapes showing 120-140 GB having good quality.
Because what we want is to reduce the total number of tapes being backed up for 
say weekly backups. So in order to reduce we will have to scrap of the bad 
quality tapes. So can u suggests how can i know the quality of the tapes from 
networker or even if there is no method , can u suggests what threshold value i 
should put for this to scrap off.

Rgds,
Kurian

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