How to turn on compression for LTO-5 under RHEL 6?

Question

How does one turn on hardware compression for LTO-5 drives under RHEL 6? I found the technical note "Configuring Tape Devices for EMC Networker" but it hasn't been updated recently. In its section on Linux it mentions 'stinit', CDI and persistent naming. So questions:

1.) As far as 'stinit'- RHEL comes with it chkconfig'ed to off and there is no example /etc/stinit.def. A fresh install of 8.0.1 causes /dev/nst0 to be used and I don't think this device name will enable hardware compression. There are three other device names (nst0a, nst0l, nst0m) but without stinit I suspect they are all going to do the same thing. These are HP drives and I can't find example /etc/stinit.def files on their site. This was a lot easier on my old platform (Solaris) where a 'c' in the device name meant compression was on.

2.) As far as CDI would this be used to turn hardware compression on or off?

3.) Is persistent naming required for RHEL 6?

I appreciate that this type of question is not part of Networker itself. But I want to use the hardware compression and I'm stuck.

Thanks

lalexis · Answer

I do not have much experience with Red Hat but it shouldn't be much different than other *NIX flavors

For me (AIX 7.1) turning on compression for LTO5 is done on the jukebox level and if I remember correctly it is the default setting.

How did you install the jukebox?

Did you use jbconfig?

lalexis · Answer

I think it is compressed by default Did you install it on the server using nsrjb?

avhays · Answer

I installed it by auto detect from NW Administrator, which I assume uses nsrjb.  It would be nice if compression was on by default.  I wonder how I could tell from Linux?  'tapeinfo'?

avhays · Answer

There is no setting to control hardware compression either from front panel or the built-in web interface on the HP MSL-2024 jukebox.  It must be done from the host.

avhays · Answer

Thanks!

lalexis · Answer

On another forum they had this discussion and although it is short it might help make sense of what you are doing.

How to set IBM LTO5 compression 2:1 to use full compressed capacity upto 3TB? - Spiceworks

It reaffirms that LTO drives use compression by default and unless the software overrides it then it will work.

From my experience NW does not override it. Most of my Oracle backups used to be half what the df -g command would list. That is until I started encrypting everything.

A word of caution: you cannot compress an encrypted file

masonb · Answer

Hi All,

I have been monitoring this thread as I had a similar question recently and just wanted to see if we reached same conclusion (which we have). I would also like to point out that unless LTO5 drives reach a speed in excess of 140MB/s the data will not be compressed (140-280MB/s). This has nothing to do with the drive/device used – it is something which the drive does via its firmware to stop shoe-shining occurring on the device which is considered worse than not compressing the data. So in order to get the 3TB compressed capacity the data path to the drive must be capable of speeds great than this. There is a chart on IBM Website which specifies this up to Generation 8

I think this still stands for HP drives also.

Regards,

Bill Mason

avhays · Answer

I am adding an appendix to this post. Under Linux I think you can verify compression by:

'sg_map' displays the /dev/sg? numbers for your scsi devices. This tells you which /dev/sg? to use for the following command.

Say /dev/sg0 is an LTO drive with a tape loaded.

'sginfo -a /dev/sg0' will display mode pages for /dev/sg0. Look for the "Data compression mode page (0xf)"

'DCE' is Data Compression Enabled. If '1' then it is enabled.

Here is a link to more about compression under Linux: http://wiki.zmanda.com/index.php/Hardware_compression

Here is link to LTO mode pages: http://www-01.ibm.com/support/docview.wss?uid=ssg1S7003555&aid=1 (google 'LTO mode pages'').

On my RHEL 6.4 system DCE was 1.

ble1 · Answer

When it comes to HW compression, it is there out of the box (assuming box is HW library and it has compression enabled).  No need to do anything on OS level (except in some cases pick proper device, but Linux does not fit that category).  However, if using IBM drives, you will find sometimes that to achieve compression you must use IBM drives which in return will create their own device handlers so you might see no compression using native Linux device names and compression only when using IBM device names.

NetWorker

How to turn on compression for LTO-5 under RHEL 6?

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