On Tue, Aug 13, 2002 at 01:38:14PM -0600, Scott Sanders wrote:
> OK I know that's a bad thing to say around here BUT...

Not around me.  I'm the lone HW compression advocate (in the right time
and place)...

> I'm backing up some Solaris 2.6 machines and need to be able to do a
> restore with nothing but the O/S CD-ROM.  Since it doesn't have gzip or
> any other compression software on the ROM I am just doing straight
> ufsdumps (level 0 every night) to tape using amanda. My question is,
> since the drive is handling the compression what tape length should I be
> specifying in my tapetype definitions? For example should I use 35000
> mbytes or 70000 mbytes for a DLT-7000 with 35GB of native capacity? Or
> maybe something in between just to make sure I don't run out f tape?

If you're otherwise happy with SW compression, your protocol could
easily be:

1)  HW compression for the OS partitions.
2)  SW compression on everything else.

You boot CDROM, restore 1), reboot and restore 2).  (AFAIK, you have to
do something like this if you're going to run VxVM or Disksuite,
anyway.)

You definitely do not want to use 70GB for tapetype length, you
will not get that much on OS partitions.

Until recently, I was running a DLT-7000, HW compression, Solaris 2.6,
and I used:

define tapetype DLT-7000HC {
    comment "DLTtape IV half-inch cartridge for DLT-7000, hardware compression"
    # assume compression ratio 0.58, length = 35000/.58 mbytes
    length 60344 mbytes
    filemark 8 kbytes
    # speed = 5000/.58 kbytes
    speed 8620 kbytes
}

This was tweaked to the max (I was stalling for as long as I possibly
could before buying a fancy new changer), and did roll off the end a
couple times in 6 months.  If I were you, and I was close to fitting on
35GB, I would use 35/.7 = 50GB.

(FWIW, I've tested the LTO drive I'm using now (HP) on the same data,
and it gets a little better than 2X (.5) compression.  Definitely
better compression HW there than on the old DLT-7000.

-- 
Jay Lessert                               jay_lessert AT accelerant DOT net
Accelerant Networks Inc.                       (voice)1.503.439.3461
Beaverton OR, USA                                (fax)1.503.466.9472