Dan Brown wrote:
During a backup, or a flush, the tape drive writes data for 4
seconds, then rewinds for 1 second, then writes for 4 seconds, then
rewinds for 1 second, etc. This seems like a good way to wear out a
drive.
That's usually a symptom of a too fast tapedrive connected
to a too slow server. But before you trow out the server, verify
that your configuration does indeed use the holdingdisk!
Not only does that lower the lifetime of the drive, it's also
immensly slow.
Amanda does quite a good job to keep the tape streaming, using
two processes with a shared memory bufferpool (one that fills
the bufferpool from the holdingdisk file, the other one that writes
the bufferpool to tape).
If you have a filesystem that is too large to be put on
the holdingdisk, amanda falls write immediately to tape. But
now the diskspeed + cputime-to-gzip + networkspeed all come
into play and probably cannot follow the tapedrive.
Your tapeserver does not have to be a monstrous expensive dragon
to keep a tape streaming. My amanda tapeserver is a Linux-PC
with a AHA2940 SCSI adapter connected to two AIT-1 tapedrives.
The tape writing speed of my backups is 2900-3100 kbytes/sec, which
is near the rated speed of the drives. The PC has only 128 Mbyte
RAM, and a 300 MHz celeron cpu. But it has a large IDE disk with
a 8Mbyte data buffer (one of the faster one in that time) of 80 Gbyte.
Our Sunfire 280 with two CPU's is not fast enough to keep the
tape streaming (gnutar speed with "compress fast" over network
about 2200 kbytes/sec), but the 10 Gbyte holdingdisk file is
taped at a rate of 3025 kbytes/sec last weekend).
Any suggestions on optimizing settings? Here are my drive configs
(minus stuff about logs, users, etc):
Really really make sure the backups use the holdingdisk.
When using gnutar, you can split up a large filesystem in smaller
ones, so that one image does fit in the holdingdisk space. If needed.
--
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
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