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.
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