Suggestions for *very fast* backup devices?
Alan's Home for Wayward Notes File.
alan at shodha.enet.dec.com
Mon May 20 03:16:26 AEST 1991
In article <1991May19.090447.8549 at ecst.csuchico.edu>, timb at 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 at nabeth.cxn.dec.com
More information about the Comp.unix.ultrix
mailing list