Inconsistent taping
I just wanted to find out if any of you have seen this. I found out that I generally could get ~70 GB on a DLT-IV tape if I used hardware compression, so I set amanda's tape length to 60 GB and started backing up big partitions. I was able to backup 55 and 52 GB partitions, but there's one 50 GB partition is particular that won't fit on a tape, apparently. I've attempted it several nights in a row, but with no success, even when amanda starts the tape with it. Is what hardware compression can do with files variable? In this case, with the failure, it's a lot of oracle data, some of it is gzipped. - - - -- Eric Trager
Re: Inconsistent taping
On Wed, 6 Mar 2002, Eric Trager wrote: Is what hardware compression can do with files variable? In this case, with the failure, it's a lot of oracle data, some of it is gzipped. This is precisely why I do not use hardware compression. The effectiveness of the compression varies heavily based on what kind of data you are backing up. Chances are 50GB of gzip'd data is not going to compress any at all. I run a fast dual PIII as my tape server and it handles doing the software compression for me just fine. With software compression planner's estimates are much more accurate and I sleep easier at night knowing that my filesystems are reliably getting taped, and if there is a problem that anything that wasn't taped was compressed and stuck in my holding disk to be flushed the following morning. My holding disk probably wouldn't hold an entire run uncompressed, but with software compression a $100 hard disk can hold an entire run. -- Brandon D. Valentine [EMAIL PROTECTED] Computer Geek, Center for Structural Biology This isn't rocket science -- but it _is_ computer science. - Terry Lambert on [EMAIL PROTECTED]
Re: Inconsistent taping
On Wed, Mar 06, 2002 at 04:59:07PM -0500, Eric Trager wrote: I found out that I generally could get ~70 GB on a DLT-IV tape if I used hardware compression, so I set amanda's tape length to 60 GB and started backing up big partitions. I was able to backup 55 and 52 GB partitions, but there's one 50 GB partition is particular that won't fit on a tape, apparently. I've attempted it several nights in a row, but with no success, even when amanda starts the tape with it. Is what hardware compression can do with files variable? In this case, with the failure, it's a lot of oracle data, some of it is gzipped. Sounds like you've answered your own question. :-) Your tape drive is either a DLT-7000 and has 35GB native capacity (or a DLT-8000 with 40GB native). If you use the HW compression device, and your data is compressible, great, you get 35GB. I've got my DLT-7000 set in my amanda.conf for 60GB. Works great for me. If your data is uncompressible, you're screwed. Your capacity is -guess what- 35GB (actually a little less). You can try SW compression, in the hope that your data is somewhat compressible and gzip can do sufficiently better (compared to the tape drive HW) to squeeze it into 35GB. You can dump/tar into a gzip/wc pipe to check that out, something like: % tar cf - /something | gzip -c --fast | dd of=/dev/null bs=1k % tar cf - /something | gzip -c --best | dd of=/dev/null bs=1k If you can't get 35GB out of this, you'll have to break the the file system up into multiple disklist entries, or buy a bigger tape drive. -- Jay Lessert [EMAIL PROTECTED] Accelerant Networks Inc. (voice)1.503.439.3461 Beaverton OR, USA(fax)1.503.466-9472
