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Operating Systems Solaris backup to tape - compression? Post 302069444 by hegemaro on Sunday 26th of March 2006 09:26:31 AM
Old 03-26-2006
Most tape device drivers in UNIX support compression at the hardware level assuming the physical tape drive supports it. Compression is enabled or disabled by specifying the appropriate tape device. Tape density can also be specified in this manner. Refer to the st(7D) man pages for a detailed list of driver options.

For example:

tar cvf /dev/rmt/0hc directory-name # high density, hardware compression

or

tar cvf /dev/rmt/0h directory-name # high-density, no compression

Remember, hardware compression rarely increases overall capacity if the data stream is already compressed. That is, if all the files in the above example "directory-name" are already compressed, enabling hardware compression won't "double compress" and could easily increase the tape required due to duplicate overhead of the software and hardware compression algorithms.
 

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st_san_safe(5)							     OBSOLETED							    st_san_safe(5)

NAME
st_san_safe - determine whether access to tape device special files without the no-rewind-on-close option is allowed (OBSOLETED) VALUES
Failsafe Default Allowed values Recommended values or DESCRIPTION
Note: this tunable is obsoleted and has been renamed to beginning with release HP-UX 11i v3. This tunable notifies the tape driver whether it should allow access to device special files without the no-rewind-on-close option. When this tunable is on the tape driver will fail any open on a tape device special file without the no-rewind-on-close option (that is, or with a status of The tunable allows the safe sharing of tape devices in SAN tape backup solution configurations. The disabling of device special files without no-rewind-on-close in a SAN tape backup solution configuration prevents the accidental sending of a rewind command on close from HP-UX systems via standard tape commands like which would corrupt a backup in process. Who Is Expected to Change This Tunable? Anyone. Restrictions on Changing Changes to this tunable take effect immediately. When Should the Tunable Be Turned On? This tunable should be turned on if the system is going to be used in a SAN tape backup solution configuration. What Are the Side Effects of Turning the Tunable On? The tape driver will fail any open to a tape device special file that does not have the no-rewind-on-close option with a status of This behavior prevents the usage of any tape device special file without the no-rewind-on-close option. When Should the Tunable Be Turned Off? This tunable should be turned off if the system is not part of a SAN tape backup solution configuration or the system utilizes will not function unless it has access to device special files without the no-rewind-on-close option. What Are the Side Effects of Turning the Tunable Off? A rewind may be issued from this system accidentally on close possibly corrupting a backup being issued from another system on the SAN. What Other Tunables Should Be Changed at the Same Time? None. WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX. Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tun- able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see at AUTHOR
was developed by Hewlett-Packard. SEE ALSO
norewind_close_disabled(5), scsi_tape(7), scsimgr_estape(7). Tunable Kernel Parameters st_san_safe(5)
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