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LTO-4 fair read margin and 5% capacity loss on new tapes

Kirill Bogdanov
Occasional Advisor

LTO-4 fair read margin and 5% capacity loss on new tapes

Dear All,

  1. I have an Ultrium 1840 SCSI drive that gives 5% capacity loss on even tracks, around 1% on odd tracks, using new HP media. I believe capacity loss should be around 0.1%, similar to what I'm getting from my old LTO-2. All wraps are recorded with "great margin" according LTT 4.16 and both off-track margin and channel variation are great margin too.
  2. Reading these tapes usually gives "good margin" and sometimes "fair margin" according to LTT 4.16. There are no retries but "C2" seems comparable to the number of sets recorded, as follows:
    Reread Datasets :0
    Reread C2 :87583
    Datasets Read :106972
    Unreadable Datasets :0
  3. I'm concerned with the head bit error rate (log10) on read, it is around -5.6 for this drive while my old LTO-2 has it around -7.5, two orders of magnitude better.

I have run a cleaning tape and got a temporary improvement: 5% capacity loss went down to 2%. After around 5 tapes it went back to where it was.

 

The drive is about a year past its warranty, what can you suggest? I can order a new head but not sure whether this will resolve the issues.

Background: the drive is some years old but with little use:
Power on time : 619 days, 19 hours, 7 minutes
Tape Pulled : 112.5 full volume equivalents
Tape Metres Pulled : 4931802 metres
Load/unload cycles : 383 (0% of expected life)
Duty cycle : 4%
Power cycles : 55
Cleans : 2
Firmware upgrades : 1

Latest firmware B63D, tried two different enclosures and controllers/cables. Read speed 111MB/sec, write speed around 106MB/sec. The box runs Debian Linux and reads data at around 170MB/sec from the array (and is rather faster to write). Temperatures for both the drive and tapes are generally "great margin" and the historical range of temperatures for the drive is 10-52 degrees. In my use, it is around 22-45 degrees.

1 REPLY
Kirill Bogdanov
Occasional Advisor

Re: LTO-4 fair read margin and 5% capacity loss on new tapes

Problem solved - sent the drive for a fixed-price repair, was told that replacement of the head is not enough, thus they sent me a refurbished unit. Everything works fine now.