PROBLEM WITH TAPE HARDWARE COMPRESSION
Hi!!! I've got an HP SURESTORE DAT 40 on my SUSE LINUX ENTERPRISE SERVER 8 BOX SP3. The tapes I use are marked 20/40GBYTE. But I can only make backup up to 20G, whereas on my ALPHA server with tru64 unix, I can save up to near 40 Gbytes using the dev file "/dev/rmt0h" (for tru64 V 4F) or "/dev/tape/tape0_d1" (for tru64 V 5.1B). I try to enable compression using the command "mt -f /dev/st0 datcompression 10", this command achieved succefully but nothing. I try to use the /dev/st0m or /dev/st0a, but these devices files seem not to be associated to physical device. So how can I perform backup with hardware compression? Please help
On Fri, 2005-12-30 at 13:18 +0000, KRAMO FIACRE wrote:
You may need to turn on compression after every reset of the tape drive. Also remember that you will never get 40G of data on the 20G tape using compression. Binary files never compress 50% and actually compress very little and some even get larger when being compressed. Also I don't recommend using software compression and hardware compression together. Please fo not use all cap letters in the subject, it will not get you any special attention in a response. -- Ken Schneider UNIX since 1989, linux since 1994, SuSE since 1998
On Fri, 30 Dec 2005, Ken Schneider wrote:
Indeed. Try using mt -f /dev/st0 datcompression 1 <<- not '10'
Also remember that you will never get 40G of data on the 20G tape using compression. Binary files never compress 50% and actually compress very
Neither of those statements are strictly true. I've seen ratios of 10:1 or better. It all depends on the nature of the data that you are backing up. Now, I don't know if hardware compression can do quite that well, but gzip certainly can, and bzip is even better (although *far* more expensive).
little and some even get larger when being compressed.
Also I don't recommend using software compression and hardware compression together.
That's good advice. -- Carpe diem - Seize the day. Carp in denim - There's a fish in my pants! Jon Nelson <jnelson-suse@jamponi.net>
RE: Hardware compression. I have some highly compressable data I backup. Sometimes the tape drive will just stop spinning for 30 seconds or more at a time. When I look to verify nothing is broken I see that data is pumping out at 20 MB/sec or more, so it is the highly compressible nature of the data that is allowing the tape drive to basically idle. Greg -- Greg Freemyer The Norcross Group Forensics for the 21st Century
On 12/30/05, KRAMO FIACRE <f.kramo@cnps.ci> wrote:
You may have to use stinit from the mt_st rpm. With my LTO-1 drive I have had to use stinit to even get it to work until SuSE 10.0. That is I am no longer calling stinit prior to using my drive, but I had to for the last couple of years with various SUSE kernels. Unfortunately the 10.0 kernel does not properly detect end of tape. So I'm running with a 2.6.14 vanilla kernel on my tape server. (It works perfect from what I can tell and still no stinit.) HTH Greg -- Greg Freemyer The Norcross Group Forensics for the 21st Century
On Fri, 2005-12-30 at 13:18 +0000, KRAMO FIACRE wrote:
You may need to turn on compression after every reset of the tape drive. Also remember that you will never get 40G of data on the 20G tape using compression. Binary files never compress 50% and actually compress very little and some even get larger when being compressed. Also I don't recommend using software compression and hardware compression together. Please fo not use all cap letters in the subject, it will not get you any special attention in a response. -- Ken Schneider UNIX since 1989, linux since 1994, SuSE since 1998
On Fri, 30 Dec 2005, Ken Schneider wrote:
Indeed. Try using mt -f /dev/st0 datcompression 1 <<- not '10'
Also remember that you will never get 40G of data on the 20G tape using compression. Binary files never compress 50% and actually compress very
Neither of those statements are strictly true. I've seen ratios of 10:1 or better. It all depends on the nature of the data that you are backing up. Now, I don't know if hardware compression can do quite that well, but gzip certainly can, and bzip is even better (although *far* more expensive).
little and some even get larger when being compressed.
Also I don't recommend using software compression and hardware compression together.
That's good advice. -- Carpe diem - Seize the day. Carp in denim - There's a fish in my pants! Jon Nelson <jnelson-suse@jamponi.net>
RE: Hardware compression. I have some highly compressable data I backup. Sometimes the tape drive will just stop spinning for 30 seconds or more at a time. When I look to verify nothing is broken I see that data is pumping out at 20 MB/sec or more, so it is the highly compressible nature of the data that is allowing the tape drive to basically idle. Greg -- Greg Freemyer The Norcross Group Forensics for the 21st Century
On 12/30/05, KRAMO FIACRE <f.kramo@cnps.ci> wrote:
You may have to use stinit from the mt_st rpm. With my LTO-1 drive I have had to use stinit to even get it to work until SuSE 10.0. That is I am no longer calling stinit prior to using my drive, but I had to for the last couple of years with various SUSE kernels. Unfortunately the 10.0 kernel does not properly detect end of tape. So I'm running with a 2.6.14 vanilla kernel on my tape server. (It works perfect from what I can tell and still no stinit.) HTH Greg -- Greg Freemyer The Norcross Group Forensics for the 21st Century
participants (4)
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Greg Freemyer -
Jon Nelson -
Ken Schneider -
KRAMO FIACRE