Gil Naveh wrote:
The issue I had was that the first time I run amtapetype the result was a
little off.
Which was painful because it takes a few hours to run it.
yet, it might not be a bug - the reason I put it in the subject was that
people would notice it.
No, it's not a bug. That's real life with tapes.
Not all tapes have exactly the same length. Even the temperature
has a measurable influence on tapecapacity.
Also when writing to tape, the drive verifies the data, and rewrites
any block that contains an uncorrectable error, up to a certain time
(15 sometimes). These "soft" errors also take up tape capacity.
Furthermore, if the drive has to pause, because the data is not
delivered fast enough to the drive, it takes a few inches to stop the
tape, rewind and restart again, leaving a little gap between the blocks
again.
That's why you should specify a little lower value than the one that
amtapetype measured.
All that said, when using an LTO drive, you may have hardware
compression enabled anyway, because the hw compr algorithm in those
drives does not expand uncompressable data. Which gives you the
opportunity to mix hardware and software compression, using whatever
method for each host/disk that fits best (slow host= only hardware
compression, slow network = software compression on client etc.)
--
Paul Bijnens, Xplanation Tel +32 16 397.511
Technologielaan 21 bus 2, B-3001 Leuven, BELGIUM Fax +32 16 397.512
http://www.xplanation.com/ email: Paul.Bijnens AT xplanation DOT com
***********************************************************************
* I think I've got the hang of it now: exit, ^D, ^C, ^\, ^Z, ^Q, F6, *
* quit, ZZ, :q, :q!, M-Z, ^X^C, logoff, logout, close, bye, /bye, *
* stop, end, F3, ~., ^]c, +++ ATH, disconnect, halt, abort, hangup, *
* PF4, F20, ^X^X, :D::D, KJOB, F14-f-e, F8-e, kill -1 $$, shutdown, *
* kill -9 1, Alt-F4, Ctrl-Alt-Del, AltGr-NumLock, Stop-A, ... *
* ... "Are you sure?" ... YES ... Phew ... I'm out *
***********************************************************************
|
