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StoreEver 6250 writes less data, than uncompressed capacity (2.5) TiB on LTO 6 tape

 
Ruben Muradyan
Occasional Advisor

StoreEver 6250 writes less data, than uncompressed capacity (2.5) TiB on LTO 6 tape

Tape Drive: StoreEver 6250 external SAS

Server OS: CentOS 7

 

Problem Description

It is not possible to write full capacity on the LTO6 tape. System throws "No space left on device" error, at random amounts of data, written on tape. Usually it is somewhere between 1.8-2.1TiB.

Tapes are brand new, device is brand new. Compression is off, data, that is being written on device is H264 compressed video.

Tried Bacula tape daemon, tar and HP LTFS with the same results.

 

Any idea what to do?

10 REPLIES 10
Dennis Handly
Acclaimed Contributor

Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TB on LTO-6 tape

Are you using encryption?  What size does the LTO-6 tape say it is?  (That's with compression.)

Ruben Muradyan
Occasional Advisor

Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TiB on LTO-6 tape

No encryption

Mounted LTFS tape is shown in df -h output with the following line:

ltfs:/dev/st0 2.3T 2.3T 0 100% /mnt/LTO6
 
 
Here's the output of ls -al
[root@localhost LTO6]# ls -al
total 1489777938
drwxrwxrwx. 2 root root 0 Jul 17 00:09 .
drwxr-xr-x. 6 root root 64 Jul 15 15:20 ..
-rwxrwxrwx. 1 root root 51764839753 Oct 26 2011 SE-DJVAR APRUST-172-HD.mov
-rwxrwxrwx. 1 root root 52879392561 Oct 27 2011 SE-DJVAR APRUST-173-HD.mov
-rwxrwxrwx. 1 root root 53035557889 Oct 28 2011 SE-DJVAR APRUST-174-HD.mov
-rwxrwxrwx. 1 root root 52603736185 Oct 31 2011 SE-DJVAR APRUST-175-HD.mov
-rwxrwxrwx. 1 root root 54184943095 Nov 3 2011 SE-DJVAR APRUST-176-HD.mov
-rwxrwxrwx. 1 root root 49461568229 Nov 2 2011 SE-DJVAR APRUST-177-HD.mov
-rwxrwxrwx. 1 root root 53122991321 Nov 3 2011 SE-DJVAR APRUST-178-HD.mov
-rwxrwxrwx. 1 root root 16242334566 Nov 5 2011 SE-DJVAR APRUST-179-SD.mov
-rwxrwxrwx. 1 root root 50950864149 Nov 7 2011 SE-DJVAR APRUST-180-HD.mov
-rwxrwxrwx. 1 root root 49236050873 Nov 8 2011 SE-DJVAR APRUST-181-HD.mov
-rwxrwxrwx. 1 root root 45829062747 Nov 10 2011 SE-DJVAR APRUST-182-HD.mov
-rwxrwxrwx. 1 root root 54686486395 Nov 11 2011 SE-DJVAR APRUST-183-HD.mov
-rwxrwxrwx. 1 root root 53506473961 Nov 11 2011 SE-DJVAR APRUST-184-HD.mov
-rwxrwxrwx. 1 root root 53783477441 Nov 14 2011 SE-DJVAR APRUST-185-HD.mov
-rwxrwxrwx. 1 root root 55170389373 Nov 15 2011 SE-DJVAR APRUST-186-HD.mov
-rwxrwxrwx. 1 root root 53084928963 Nov 16 2011 SE-DJVAR APRUST-187-HD.mov
-rwxrwxrwx. 1 root root 56821972593 Nov 17 2011 SE-DJVAR APRUST-188-HD.mov
-rwxrwxrwx. 1 root root 57548038559 Nov 18 2011 SE-DJVAR APRUST-189-HD.mov
-rwxrwxrwx. 1 root root 55214636369 Nov 21 2011 SE-DJVAR APRUST-190-HD.mov
-rwxrwxrwx. 1 root root 53360771755 Nov 22 2011 SE-DJVAR APRUST-191-HD.mov
-rwxrwxrwx. 1 root root 57145088969 Nov 23 2011 SE-DJVAR APRUST-192-HD.mov
-rwxrwxrwx. 1 root root 58301161261 Nov 24 2011 SE-DJVAR APRUST-193-HD.mov
-rwxrwxrwx. 1 root root 54067344631 Nov 28 2011 SE-DJVAR APRUST-194-HD.mov
-rwxrwxrwx. 1 root root 57983784439 Nov 29 2011 SE-DJVAR APRUST-195-HD.mov
-rwxrwxrwx. 1 root root 56307255247 Nov 30 2011 SE-DJVAR APRUST-196-HD.mov
-rwxrwxrwx. 1 root root 55292488671 Dec 1 2011 SE-DJVAR APRUST-197-HD.mov
-rwxrwxrwx. 1 root root 53988433171 Dec 2 2011 SE-DJVAR APRUST-198-HD.mov
-rwxrwxrwx. 1 root root 48776914827 Dec 5 2011 SE-DJVAR APRUST-199-HD.mov
-rwxrwxrwx. 1 root root 53500254831 Dec 6 2011 SE-DJVAR APRUST-200-HD.mov
-rwxrwxrwx. 1 root root 7681359872 Jul 17 00:11 SE-DJVAR APRUST-201-HD.mov
[root@localhost LTO6]#
 
The last file is incomplete, because of insufficient space.
The amount of data, written to this particular tape is 1,454,861 MB.
 
Dennis Handly
Acclaimed Contributor

Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TB on LTO-6 tape

>Mounted LTFS tape is shown in df -h output with the following line:

 

Sorry, what I meant what does the marketing words say about the tape?

I.e. the wrapper around the product when you buy it.

If it says X, you really have X / 2 if it is uncompressed.

Ruben Muradyan
Occasional Advisor

Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TiB on LTO-6 tape

It's a standard LTO6 cartridge.

Photo attached

Dennis Handly
Acclaimed Contributor

Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TB on LTO-6 tape

Ok, 6.25 vs 2.5.  Why do you think this is in TiB?  Typically storage is marketed in TB only.

Also, if you can't feed the data fast enough, you may get less on the tape.

Torsten.
Acclaimed Contributor

Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TB on LTO-6 tape

The marketing 2.5TB are 2.27TiB minus some overhead depending on your application, so your 2.1TiB value looks not so bad, IMHO.


Hope this helps!
Regards
Torsten.

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Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TB on LTO-6 tape

The achieved capacity sizes you report seem small but it is hard to say how much was actually written to tape without some data from the tape drive.

 

Tape has two capacity points, early warning (EW), and end of tape (EOT).  EW is reported before the full capacity is used up so software that stops writing at EW will always get a little less than the advertised capacity but it should be really close.  As has been mentioned 2.27 TiB is about what you should expect to be the maximum.

 

If you use the HP Library and Tape Tools utility (http://www.hp.com/support/tapetools) you can pull a "Support Ticket" from the drive at the conclusion of a job and post that here.  The support ticket will contain information about the amount of data written to the tape along with performance and retry information that can help determine if there is some reason that you aren't getting the expected capacity.

Accept or Kudo

Ruben Muradyan
Occasional Advisor

Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TB on LTO-6 tape


@Dennis Handly wrote:

Ok, 6.25 vs 2.5.  Why do you think this is in TiB?  Typically storage is marketed in TB only.

Also, if you can't feed the data fast enough, you may get less on the tape.


I do not think, that it is in TiB.

 

My main problem is, that I get random not standard (varying from 1,4TiB to 2,1Tib) capacity.

 

I'm feeding data from a RAID10 disk, that handles 700MB/sec RW, and there are no I/O at the time of writing to tape.

 

Ruben Muradyan
Occasional Advisor

Re: StoreEver 6250 writes less data, than uncompressed capacity (2.5) TB on LTO-6 tape


@Torsten. wrote:

The marketing 2.5TB are 2.27TiB minus some overhead depending on your application, so your 2.1TiB value looks not so bad, IMHO.


It is the MAX. Usually I get ~1.7TiB.

But the main issue is, that size of the tape is unpredictable. I can write there 1.5TiB, 1.7, 1.4, etc.

While this system is used for archiving, not for backup, it is critical to be able to predict  what to expect from media.