110T DLT VS 80: Compressed Mode with 'mt' command??

epperson@alumni.unc.edu epperson at alumni.unc.edu
Thu Mar 3 09:45:01 CST 2005


On Thu, March 3, 2005 6:02 am, Xavier Poinsard said:
> Thomas E. Besemer wrote:
>> I've got a PowerVault 110 DLT VS 80, and I'm using dump to perform
>> backups
>> on it.  Dump fails (asked for media change) at 40 GB, I assume that the
>> drive does not come up defaulted to hardware compression on???
>>
>> Does anybody know how to how to put compression on with 'mt'??
>
> I am using :
> /bin/mt -f /dev/nst0 setdensity 0x87
>
> The following command should give the correct values.
> mt  -t /dev/st0 densities
>
Of course, compressibility of data varies, and can do so within a fixed
size file.  For instance, we find that an 80Gb. Oracle dbs file can fit
nicely on such a tape initially, but as transactions populate it with
data, it may no longer compress to the 40Gb. native size of the tape. 
Causes no end of headaches, particularly with one application that makes
the mistake of storing already compressed images inside the database
instead of storing them as files, with pointers in the database.  The
point is, this could be happening with compression turned on.




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