richk@tera.com (Richard Korry) (05/10/91)
I'm curious about people's retry rates on a Exabyte on a Sun 4/490. I tried three tapes and got the following numbers for a daily dump of around 150Mb: Sony P6-120MP: 420 (Tape is about 3 months old, tenth use) Maxell HS-8/112: 192 (tape is brand new, 1st use) Exabyte-112: 222 ( tape is 6 months old, 5th use) These seem high. Should I get Sun to come out and look at it? Thanks.
bovet@hao.ucar.edu (Ray Bovet) (06/05/91)
In article <2847@brchh104.bnr.ca> richk@tera.com (Richard Korry) writes: >X-Sun-Spots-Digest: Volume 10, Issue 98, message 18 >X-Note: Submissions: sun-spots@rice.edu, Admin: sun-spots-request@rice.edu > >I'm curious about people's retry rates on a Exabyte on a Sun 4/490. I >tried three tapes and got the following numbers for a daily dump of around >150Mb: > >Sony P6-120MP: 420 (Tape is about 3 months old, tenth use) >Maxell HS-8/112: 192 (tape is brand new, 1st use) >Exabyte-112: 222 ( tape is 6 months old, 5th use) > >These seem high. Should I get Sun to come out and look at it? Thanks. The summary says it all! What matters is the retry rate. A certain number of retries on writing is normal and entirely to be expected. An Exabyte writes data in 1 kbyte blocks to the tape. So 150Mb is 150k blocks. Your error rates are about: Sony P6-120MP: 0.28% Maxell HS-8/112: 0.13% Exabyte-112: 0.15% I _like_ to see numbers of a few tenths of a percent (like 0.1%) but I don't worry unless it is quite a bit higher. Remember that the retries on write is how many times the read after write using a reduced read threshhold found errors and rewrote the block to make sure it is perfect on the tape. Read retries refer to how many times the drive had to make use of the 400 some bytes of ECC written out with each 1 kby block of data to get it correct. Two additional comments about error rates. First, they _do_ go up if you don't clean your drive regularly (using only the official Exabyte cleaning kits). Second, the error rate on tapes generally drops for the first few uses of the tape and then slowly begins to rise. Brand new tapes typically have "manufacturing debris" on them which gets cleaned off the tape with use. Ray