Forum Discussion

Hanzo581's avatar
Hanzo581
Level 4
11 years ago

Number_Data_Buffers Question

So recently we made the move to SLPs.  We write to a virtual tape via a VTL and at the same time in the SLP we have duplications for two physical tapes.

Everything is going fine, all the SLPs and duplication finish fine, but today we noticed one ran way longer than it has in the past.  Looking at the details it showed.

1/6/2014 9:58:59 AM - Info bptm(pid=8972) media id FC4076 mounted on drive index 44, drivepath /dev/alias/nst/F0020EC025, drivename IBM.ULTRIUM-TD4.060, copy 3
1/6/2014 1:01:11 PM - Info bptm(pid=9556) waited for empty buffer 199 times, delayed 382394 times   
1/6/2014 1:01:11 PM - end reading; read time: 03:19:08
1/6/2014 1:01:11 PM - positioning FC5520 to file 2
1/6/2014 1:01:11 PM - positioned FC5520; position time: 00:00:00
1/6/2014 1:01:11 PM - begin reading
1/6/2014 1:56:17 PM - Info bptm(pid=9556) waited for empty buffer 56 times, delayed 105814 times   
1/6/2014 1:56:17 PM - end reading; read time: 00:55:06
1/6/2014 1:56:17 PM - Info bptm(pid=8972) waited for full buffer 605 times, delayed 1159589 times   
1/6/2014 1:56:19 PM - Info bptm(pid=8972) setting receive network buffer to 262144 bytes     
1/6/2014 1:56:19 PM - positioning FC5520 to file 3
1/6/2014 1:56:19 PM - positioned FC5520; position time: 00:00:00
1/6/2014 1:56:28 PM - Info bptm(pid=9556) completed reading backup image        
1/6/2014 1:56:28 PM - Info bptm(pid=9556) EXITING with status 0 <----------       
1/6/2014 1:56:36 PM - Info bptm(pid=8972) EXITING with status 0 <----------       
1/6/2014 1:56:36 PM - end Duplicate; elapsed time: 10:07:24
the requested operation was successfully completed(0)

 

We then looked deeper and a large amound of SLPs have similar waiting for empty/full buffer lines.

 

So after some searching, it looks like we need to raise our buffer number, right now our NUMBER_DATA_BUFFERS is set to 32 while our SIZE_DATA_BUFFERS is set to 262144 (support had us set this to this number for path to tape to work).

 

Should changing from 32 to 64 or 128 help with this?

 

Thanks!

 

7.5
Backup and Recovery
NetBackup
Windows Server (2003-2008)
  • Nicolai's avatar
    Nicolai
    11 years ago

    No No No

    Small buffer will only add to the tape drive effect called "shoe shining".

    Is better to send one 256K buffer (bucket) to the tape drive than sending 4*64K. Worst case scenario you need to do 4 start/stop operations for 64K block size  instead of just one using 256K.

    When counting buffers wait you need to look at the average value on all jobs. Some jobs will always misbehave ....

19 Replies

Sort By
Show More
  • Hanzo581's avatar
    Hanzo581
    Level 4
    11 years ago

    Sorry, forgot to answer the question.  Yes, SIZE_DATA_BUFFERS is set to 262144 on all servers, master and media in the environment.

  • Sat-Chit-ananda's avatar
    Sat-Chit-ananda
    Level 3
    11 years ago

    Check this post, you may have soultion your issue.

    https://www-secure.symantec.com/connect/forums/disk-based-data-backup-and-tape-storage-based-recovery-get-best-out-your-tape-drives

  • Sat-Chit-ananda's avatar
    Sat-Chit-ananda
    Level 3
    11 years ago

    Hmm, I am new to this forum.

    I tried to create it as blog, some how it doesn't go to published state.posted it as a forum discussion,Some one had objection certain content.

    Edited it and posted my contents only.Below is the blog link.

    https://www-secure.symantec.com/connect/blogs/disk-based-data-backup-and-tape-storage-based-recovery-get-baest-out-your-tape-drives

  • KDob's avatar
    KDob
    Level 3
    11 years ago

    Hmm.

     

    "waited for full buffer 116 times, delayed 222273 times"

    Seems like it is waiting for FULL buffers.  shouldn't that indicate that the buffer size should be smaller, and not larger?  There should be fewer buckets of smaller size, that way there would be a reduction in the time to wait for the buckets to get full?

    Curious,

  • Nicolai's avatar
    Nicolai
    Moderator
    11 years ago

    No No No

    Small buffer will only add to the tape drive effect called "shoe shining".

    Is better to send one 256K buffer (bucket) to the tape drive than sending 4*64K. Worst case scenario you need to do 4 start/stop operations for 64K block size  instead of just one using 256K.

    When counting buffers wait you need to look at the average value on all jobs. Some jobs will always misbehave ....

  • mph999's avatar
    mph999
    Level 6
    11 years ago

    Nicolai is right, but your idea of smaller bukets is logical - a good question.

    The problem with smaller buffers, is they get full quicker yes, but also empty quicker.

    It's a fine balancing act, and as you see, virtually impossible to explain in a reasonable space to cover all possibilities.