timb@ecst.csuchico.edu (Timothy Berger) (05/19/91)
What devices and/or specific hardware out there can make backups a *fast* and reliable procedure? I realize how general this is -- I'm looking for past experiences (good or bad) and suggestions. Thanks, Tim B.
alan@shodha.enet.dec.com ( Alan's Home for Wayward Notes File.) (05/20/91)
In article <1991May19.090447.8549@ecst.csuchico.edu>, timb@ecst.csuchico.edu (Timothy Berger) writes: > What devices and/or specific hardware out there can make backups a *fast* > and reliable procedure? I realize how general this is -- I'm looking for > past experiences (good or bad) and suggestions. The problem with dump(8) is that it doesn't read from disk fast enough to keep the fastest tape drives busy. For example, on a VAX 8800 reading from an RA90 connect to KDB50 or HSC70 and dumping to /dev/null about the best dump(8) can do is 400 KB/sec. Therefore, this is about as fast as it can write to tape. In the case of writting to a TA90 the 10KB block size that most tape things use is far from ideal. I've found 48 KB to be a good choice, but restore doesn't like to read back anything but 10 KB. If you use a very fast disk, preferably non-rotating then dump(8) can read very quickly and write to tape nearly as quickly. Just this morning on the above VAX 8800 I dumped a file system on a KDB50 connected ESE20 to an HSC70/CIBCA-A connected TA90 and got about 500-700 KB/sec. You could probably get similar rates on disks with a read-ahead cache. If the disk reads a track or two at a time, then many of the file system blocks you need as you go wandering across the disk are readily available and you don't have rotational waits. I'm not sure what fast tape drives are available. The TK50 is clearly out. The TK70 is a little better. The TF857 isn't supported by ULTRIX, though it appears to be fairly fast. The TLZ04 RDAT goes at best around 150 KB/sec. I'm not sure about the 8mm we support. I've heard that some of the newer ones are up in the 500 KB/sec range. About the best write speed for a TA90 that I've seen is 1 MB/sec, using tapex(8). The models that do compression may be different. The read speed was 1.48 MB/sec and probably limited by my CI adapter. Dump(8) relies on the inherent reliability of the tape drive to make backups reliable. There may be 3rd party backup programs that do the CRC and XOR block like things that VMS BACKUP uses, but that will tend to hurt performance. > > Thanks, > > Tim B. -- Alan Rollow alan@nabeth.cxn.dec.com