RE: archive compression question

Carlton - I've been using 8mm drives for years. I've used them with and without the on-board h/w compression. I've found that using the H/W compression, not only increases the capacity per tape, but also increases overall through-put/transfer rate. Using an 8mm, with compression, I can cut the time to complete a traditional tb/ontape backup in half. As far as compression ratio's go, it's all data dependent (what did you expect ?). In my case, I've found that in using a ratio of about 1.7 is safe with tb/ontape. I could probably get more, but run the risk of blowing-out the end of tape, and hence the backup. Of coarse calculating a 'reasonable' compression ratio, and tape size isn't necessary with onarchive. One additional comment though.....Informix's official standpoint on the use of compression tape drives (last I heard), was that it is NOT supported. This had always been their position, with pre DSA versions. With DSA, onarchive introduced S/W compression, as part of OnArchive. I questioned Informix about a year ago, whether h/w compression is now supported, since they do in OnArchive. The answer I got, was still no. Now I have a hard time with this, and even got our hardware vendor involved. The tape drives we use, require no special ioctl's, no special commands, etc. The use of compression, is determined by the device selected. Informix should not have care one, whether or not your using a compressed drive....it doesn't know. As long as the drive uncompresses on the way out, what it compressed on the way in. Anyway, yes h/w compression works. It increases tape capacity, and improves overall backup performance. It's faster then tying up cycles using OnArchive s/w compression. It's just not supported. Jon ------------------------------ Jon C. Vemo jvemo@cyberspace.com Bothell, WA U.S.A. ---------- From: DBA Resources[SMTP:dbaresrc@xmission.com] Sent: Friday, October 27, 1995 10:05 AM To: informix-list@rmy.emory.edu Subject: archive compression question We are looking at getting either a 4mm or an 8mm device to do OnLine archives. Each of these devices has on-board hardware compression that can double or triple the native capacities of the drives. My question is this -- will the data stream coming out of the engine com- press or is it like a gif file that is as compressed as it can get? If anyone has experience with this I would appreciate the help. Thanks Carlton ______________________________________________________________________ Carlton Doe "It's not *over* until I win!" DBA Resources, Inc. -- Les Brown Salt Lake City, UT carlton@errin.dbaresrc.com http://www.xmission.com/~dbaresrc dbaresrc@xmission.com PGP key: finger -l dbaresrc@xmission.com