Media Statistics 1

[polymorphicAlpha]

We are using 35/70 GB DLT tapes on a Compaq TL891 robotic tape library. In BE, when viewing the stats on any particular media, it will show extremely large data writes. On a particular 35/70 GB dlt, it shows up as 215,545.355 MB. 215 GB???!!!! On a 70 GB maximum tape??? What is the deal? Does BE just report incorrect data writes? Is it incapable of actually keeping track of data writes?

 

[PHead2]

I'm pretty sure this figure notes the total amount of data written to the media - if it's been overwritten at all then the number can end up being well above the actual capacity of the media.

 

[SQLBill]

The information it's showing is from the HEADER. So, that means the backup was that large and therefore it most likely spanned two or more tapes.

Go to the RESTORE SELECTIONS tab. You should have a list of your restore options. Select the one that you are interested in and right-click to select Properties. Then select the Media tab. That will show any other tapes that the backup spanned.

-SQLBill

 

[jamkey]

If you are looking at the properties of a piece of media and are on the "Statistics" tab you should notice that it says "Totals". If you want the current amount of data on tape, go to the reports tab and run the Media Set report (this also gives total as well, but the very last column is the current MB). Is that what you actually were looking for?

 

[polymorphicAlpha]

The current total data on the tape is what I'm looking for, yes. This particular backup only occupies this one tape and doesn't span any others.

jamkey, I'll check the media set report and see if that gives me what I want.

Thx guys!

 

[polymorphicAlpha]

Heh, the media report says the tape has 201 GB total written to it. The current size, which is what I was looking for, is 96 GB...far above the 70 GB maximum size of the tape! Weird.

 

[CartagenaSoftware]

I just want to clarify that 70 GB is not the maximum size of the "35/70" tape. 35 GB is the native capacity of the tape, which is a maximum. 70 GB is an estimate of the compressed data that will fit, assuming that the compression ratio is 2:1. However, the compression ratio is data dependent, and may vary considerably. If your full tape holds 96 GB, then you are getting 2.74:1 compression, which is very possible. If you backup a different set of data, you may get a different compression ratio again, and therefore a different amount of data will fit onto the tape. It can be more or less than 70 GB.

 

[polymorphicAlpha]

True, and that's what I meant...ie, 35/70 GB. But, even with 10000:1 compression, the tape can only phisically hold 70GB of data, right? You couldn't compress 1GB to 500MB and fit that on a floppy, could you? If 70GB is the maximum compression ratio to data, then the maximum amount of data you could fit on the tape would be 70GB....or am I missing something?

 

[CartagenaSoftware]

The tape can only physically hold 35 GB, which is a physical limit. 70 GB is not a limit, it is an estimate based on a 'typical' (Not maximum!) compression ratio of 2:1. So if you experience 2.74:1 (higher than 2:1) compression ratio, you can store *more* than 70 GB on the tape, eg. 96 GB. You are not likely to achieve greater than 10:1 compression in a real application. At 10:1, the tape could store 350 GB. The number will more likely be 'near' 70 GB. (eg. 96 GB!)

 

[jamkey]

CartagenaSoftware is exactly right. Think of it like a 35GB hard drive with compression turned on. If you write 35gb of zipped files to it you will only get 35GB of data on it (unless you are calculating the data once it is unzipped to another location). If you write text files or uncompressed MDB (access database) files you could get well over 100GB of "data" on the drive. The industry says 35/70 but the 70gb is totally theorectical and assumes an agreed "industry standard" presumtion of a 2:1 compression ratio (while the average is actually closer to 1.6:1 in my experience). In some uncommon cases, where a large uncompressed drive of data is being backed up, you'll see better than the "presumed" 2:1 compression ratio, as in your case, but again, this is uncommon.

 

[SQLBill]

In addition to what CarragenaSoftware said....Veritas' media header can show more data size than what is really there. I have a 192 GB database, but when I cataloged the tape it shows 330 GB for that database. I asked Veritas about it and they say 'that is allocated space'. They also said it can vary depending on how many processors you have (we have four), but what the number of processors has to do with it they didn't say. They also blamed it on MS SQL Server.

But the bottom line is that it's the amount of space Veritas thinks it needs to restore the data. By the way, that was 330 GB on a 100/200 LTO tape, when in reality our five databases were around 220 GB of actual data.

-SQLBill

 

[polymorphicAlpha]

Thanks, guys, that's good to know. Now, I'm taking all of what you say to heart, yet I still don't fully comprehend it.

In essence, there is no limit on the amount of data I can store on a 35GB tape??? Because, as it stands, I can fit 129GB on a 35GB tape so far, according to BE.

 

[CartagenaSoftware]

When you store 129 GB on the 35 GB native capacity tape, your compression ratio is 129/35 = 3.7 (approximately). That is still normal. For practical purposes, you could consider 10:1 to be a maximum compression ratio, which would impose a 'practical' limit of 350 MB on your tape.

If you want to consider theoretical limits, you could artificially construct a very compressible string of data, say all zeroes or all ones, in which case you could store an almost infinite amount of data on the tape! It would be very boring data to back up and to restore, and a boring wait during that time. But it would be very compressible.

http://www.cartagena.com

 

[CartagenaSoftware]

Sorry, should be 350 GB, above.

 

[zoeythecat]

This is all very good info. If I could ask someone to explain my situation. I have a 35GB tape system (Internal), backing up folders/files that come out to 22GIG but my backup goes up to 35GIG and then asks for another tape. If what I am understanding from everyone who responded here I should be able to backup beyond the 35GIG limit? Am I missing something? I have backupexec 8.6 and when my tape reaches 35GIG (And I do have compression on)it stops and asks for another tape. Is there a way to setup compression in my situation to allow the tape to go beyond the 35GIG limitation?

TIA

 

[polymorphicAlpha]

zoeythecat, that's what I find strange. One of my particular SQL databases is over 220GB. The entire dbase gets backed up on 2 35GB tapes. It's weird that yours is asking for another tape.

 

[zoeythecat]

PolymorphicAlpha,

Right. Am I missing a setting somewhere? Would love to compare the compression properties. Maybe I am leaving some compression setting out somewhere?

 

[polymorphicAlpha]

Actually, I haven't even messed with any compression properties...if there ARE any.

 

[polymorphicAlpha]

Ok, if you choose your drive/library, right click, go to properties and hit the Configuration tab, there is an option for "Enable Hardware Compression". If it is not available your drive doesn't support compression. You'll have to use software compression on the jobs themselves. Otherwise, tick this option and leave the defaults. That's what my config is set to.

 

[zoeythecat]

Thanks. I do have that checked. I think compression is working (2 to 1, I think?). When I add up the folders/files that are backed up it comes out to 22GIG but the tape reaches to 35GIG and then I get prompted to insert another tape. Guess I was hoping there was some way to go beyond that 35GIG for 1 tape.