Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?
2010-08-13 16:56:46
> From: Phil Stracchino [mailto:alaric AT metrocast DOT net]
> Sent: Friday, August 13, 2010 7:51 AM
> To: bacula-users AT lists.sourceforge DOT net
> Subject: Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or
> Software compression?
>
> On 08/13/10 04:10, Dietz Pröpper wrote:
> > IMHO there are two problems with hardware compression:
> > 1. Data mix: The compression algorithms tend to work quite well on
> > compressable stuff, but can't cope very well with precompressed
> stuff, i.e.
> > encrypted data or media files. On an old DLT drive (but modern
> hardware
> > should perform in a similar fashion), I get around 7MB/s with
> "normal" data
> > and around 3MB/s with precrompessed stuff. The raw tape write rate is
> > somewhere around 4MB/s. And even worse - due to the fact that the
> > compression blurs precompressed data, it also takes noticeable more
> tape
> > space.
> > 2. Vendors: I've seen it more than once that tape vendors managed to
> break
> > their own compression, which means that a replacement tape drive two
> years
> > younger than it's predecessor can no longer read the compressed tape.
> > Compatibility between vendors, the same.
> > So, if the compression algorithm is not defined in the tape drive's
> > standard then it's no good idea to even think about using the tape's
> > hardware compression.
>
> Neither of these issues is applicable to LTO. The compression
> algorithm
> (which is a pretty good one) is defined in the LTO specification, and
> the drive compresses data block-by-block, doing a trial compression of
> each data block and writing whichever is the smaller of the compressed
> and uncompressed version of that block to tape, flagging individual
> blocks as compressed or uncompressed.
>
> --
> Phil Stracchino, CDK#2 DoD#299792458 ICBM: 43.5607, -71.355
> alaric AT caerllewys DOT net alaric AT metrocast DOT net phil AT
> co.ordinate DOT org
> Renaissance Man, Unix ronin, Perl hacker, Free Stater
> It's not the years, it's the mileage.
>
Remember also that if you are trying to minimize tape/disk/other backup media
space used, and using encryption, you will need to use software compression.
The FD compresses before encrypting; once encrypted, as noted above, the data
is no longer compressible...
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- [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, Mike Hanby
- Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, Phil Stracchino
- Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, Mike Hanby
- Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, Dietz Pröpper
- Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?,
Peter Zenge <=
- Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, John Drescher
- Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, Dietz Pröpper
- Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, Phil Stracchino
- Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, Dietz Pröpper
Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, John Drescher
Re: [Bacula-users] Dell PV-124T with Ultrium TD4, Hardware or Software compression?, Craig White
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