cancel
Showing results for 
Search instead for 
Did you mean: 

Question Regarding Tape and Drive Density

jshoker
Level 3
Hi,
 
I recently changed a configuration with a LTO1 drive and all the the settings in the policies and storage units with hcart density selected, to a LTO3 drive. I am using LTO2 Media. Now I am confused a bit regarding the density. Some people have said that the the hcart settings are just labels and they do not determine how much data actually goes on the drive. Is this true? I am starting to doubt this, because I had a backup that had about only 170GB backed up on tape in  a standalone drive, eject the tape and request another. There shouldn't have been any data still retained on the tape so I don't know why it was requesting another tape since it was an LTO 2 tape. All I can think was that it was that the drive and tapes were designated hcart when they are respectively LTO3 and LTO2. Anybody shed some light on the density designation so I can either rule them out or change the settings? Also If I want to change the settings how do I do it for the media itself. I figured out how to change the settings for the drive and the storage units.
 
Thanks in advance,
jt
10 REPLIES 10

Randy_Samora
Level 6
I'm not sure why the 170GB job asked for another tape unless it has something to do with your compression settings and what kind of data you are writing to tape.  I do know that the density setting has nothing to do with tape capacity. If "A BUNCH" was listed in the density drop down box, you could select that setting and it wouldn't change a thing.  I started used DLT back when my libraries were DLT.  I have gone from DLT, to SDLT, to LTO2 and my density has always remained DLT just because it was easier to leave it that way.
 
I just looked at my eject list from my weekend backups and I have data ranging from129GB on one tape to 414GB on another tape and everything in between.  It just depends on what kind of data you are backing up.  Can you tell me what your compression settings are?  Now you have me wondering about my own tapes.

jshoker
Level 3
Hi,
 
Are you talking about the compression within the policies? I have that turned off. When I originally set up things serveral years back, if I recall correctly, that was just for software compression. I didn't want to add extra load to the clients and I was also informed that the software compression adds to the job time. I assumed that the hardware compression was on. Maybe I am wrong here.
 
 
jt

Randy_Samora
Level 6
You are correct on the assumptions about software compression; I never use it.  But I have hardware compression activated on my tape drives.

jshoker
Level 3
Randy,
 
How can I check to see if the hardware compression is enabled on my drive? Is it a funciton of the drive or the software. I was told the software controlled it, but I can't recall where this is set in Netbackup.

Darren_Dunham
Level 6
Drive (hardware) compression isn't generally controlled directly by NetBackup.  What OS are you using?

On Unix systems, it's usually controlled by the access device for the tape.  One tape drive might have several different "names" in the filesystem, each of which differ slightly by tape format and compression settings.  NetBackup will simply use the device you give it.

As an example, a Solaris machine might use /dev/rmt/0cbn to refer to a drive with compression and at the highest capacity format, but /dev/rmt/0lbn might be the same device at a lower capacity format and with compression turned off.  The specifics depend on the drives and the OS.

LTO drives only have one format valid for a tape (this is different than some others like DLT), so the only knob you have on the device is setting the compression on or off.

--
Darren

jshoker
Level 3
I am on Windows Server 2000 with Netbackup 5.1. The drive I am using is a Dell 110T LTO3 drive (IBM Ultrium TD3 5480). I can't see anything on the unit that enables or disables it.

sdo
Moderator
Moderator
Partner    VIP    Certified
Isn't getting 170GB on an LTO2 actual possible, I mean, I know it looks low, but it is entirely possible that the limit of the tape was reached.  LTO2 theoretical max is 200GB to 400GB.  If the data stored is not compressible, then you'll get around 200GB on the media, but only if it was streaming.  If the drive wasn't fed quickly enough you'll have zillions of IRG (inter record gaps) in the tape where the tape had to stop, rewind and re-position to a point just after the last write - so, it is quite feasible that you only have 170 GB on a volume.
 
Is there just one tape with this symptom?  Or many?
What the maximum on any one of the other tapes of the same brand/batch/set?
 
I have LTO1.  My average in one library is 180GB, and the average in the other library is 205GB/media (out of 600 media in each library) - some of my LTO1 media have over 500GB on them, therefore I must have several with much less.

jshoker
Level 3
Well I have only one tape drive and so I can't really say if the problem is with just this tape drive. I have basically two policies running. One backs up a Solaris box with a bunch of project data and the other is Windows box. The servers are on a Gigbit network so I don't know if they are not getting enough data. How can I diagnose something like this?

sdo
Moderator
Moderator
Partner    VIP    Certified
I was wondering if you have a problem with one or more specific media from a brand or batch, not the drive itself.
 
I've just checked my media, and I have:
< 180 at site A     192  (out of 531 full media)
< 180 at site B     270  (out of 479 media)
< 180 at Offsite      57 (out of 125 media)
 
So I do have lots of full LTO1 media with less than my average capacity of 180, one as low as 97 GB.

jshoker
Level 3
Media problem could be the case because the same jobs ran fine last night. I am quite sure that the data didn't decrease. In fact it probably increased. The brand of media in the drive is the same so, it maybe just that particular tape. I guess I will have to keep an I out on things. Thanks all for your input.