Running exchange server version 5.5 service pac 3 With NBU 3.4 patched to
645 patch level



  Problem summary: 

    When performing individual mailbox backups on a large information 
  store, the 
    throughput decreases to the point they run too slowly to be practical. 
  On a 
    smaller information store, the throughput is slow, but it remains high 

    enough to be usable. 

    Throughput on these same two clients is absolutely fine during normal 
    backups.  Following are some sample throughput averages: 

    Job Type        SmallExchangeServer     BigExchangeServer 
    IS/DS backup    3.6 meg/sec             3.1 meg/sec 
    NT file system backup   2.2 meg/sec     1.9 meg/sec 
    HKLM backup     1.3 meg/sec             1.3 meg/sec 
    Mailbox backup  700 k/sec               350 k/sec 

    It should be noted that all the results are obtained from backups 
  during 
    off-peak hours.  There are generally other backup jobs which utilize 
  the 
    same library and master server which run during all but the 
    BigExchangeServer mailbox backup, so the above throughputs for 
  everything 
    but the mailbox backups of BigExchangeServer would be quicker if they 
  were 
    running alone.  The information store on SmallExchangeServer is 4 gig, 
  and 
    the information store on BigExchangeServer is just over 26 gig. 

    Both the backup server and BigExchangeServer have two dual-port NICs 
  (forced 
    100/full) and have an ether-channeled bandwidth of 400 mb/sec. 
    SmallExchangeServer is a single NIC set at 100/full. 

    General mailbox backup behavior: 

    Mailbox jobs on BigExchangeServer start out at roughly 700 k/sec; 
  however, 
    they slow down to 350 k/second (and at times less) as the backup 
  progresses. 
    I also have problems with timeouts.  I've bumped both the client and 
  server 
    read timeouts up to 15 minutes, but have continued to experience 
  timeout 
    problems.  They seem to manifest themselves more frequently on larger 
    mailboxes.  I just bumped both timeout levels up to 20 minutes; 
  however, I 
    will need to wait until next weekend to test this setting. 

    Mailbox jobs on SmallExchangeServer start out over 1 meg/sec and 
  eventually 
    slow to 700 k/sec.  I have not experienced timeouts on this server, 
  and have 
    kept it at the default timeout setting of 5 minutes. 

    Troubleshooting: 

    One suggestion I was given was to use multiple data streams.  The 
  problem 
    with this is that multiple data streams will not work with the 
  standard job 
    directive of "Microsoft Exchange Mailboxes:\".  I have not found a 
  wildcard 
    method, such as "back up all mailboxes beginning with 'a'" that will 
  work to 
    split the job up in a reasonable manner.  Thus, the only way to get 
  multiple 
    data streams to work is to reference each mailbox individually as a 
  separate 
    line item in the directive list and intersperse that with new stream 
    directives.  This isn't practical with over 400 mailboxes! 

    Unfortunately, due to the excessively slow throughput on the large 
    information store's mailbox backups, I cannot perform a complete 
  mailbox 
    backup in a reasonable period of time.  It would take over three days 
  at the 
    average rate of 350 k/sec for this job to complete, which means I 
  can't even 
    set it up for the weekend.  I also cannot perform incrementals on 
  mailboxes, 
    per the Admin Guide.  Thus, I have no options for getting a complete 
  mailbox 
    backup on this server, other than defining each mailbox individually. 


    It should be noted that when multiple data streams are employed by 
  providing 
    specific directives, the overall throughput does increase somewhat. 
  Two of 
    the largest mailboxes which, when backed up by themselves, have a 
  throughput 
    of roughly 700 k/sec on BigExchangeServer have a combined throughput 
  (via 
    concurrent data streams) of 950 k/sec (not a huge improvement, but 
  enough to 
    show that the server itself it capable of handling more).  I've also 
  run 
    perfmon on that server during backups to ensure it isn't being pegged 
  too 
    hard, and everything is running under acceptable levels. 

    Backups of a handful of mailboxes at a time can result in much better 
    throughput on both servers (for obvious reasons); however, anytime the 

    amount of data increases, the overall throughput decreases 
  significantly.  I 
    do understand that mailbox backups access the database in such a way 
  that 
    they will be slower than IS/DS backups, and I also understand the 
  reasoning 
    behind why the slowness gets worse the larger the amount of data 
  backed up. 
    My questions are not in regard to why this is happening, but rather, 
  why the 
    slowness is so severe.  Another question would be what Veritas's 
  comments 
    are on what throughput that should be expected with what size 
  information 
    store.  Is what I'm seeing standard, or is it below normal?  It seems 
  as 
    though I shouldn't be running into limitations with only a 26 gig 
    information store, as this really isn't excessively large for an IT 
  shop. 

    Thanks in advance for any help you can provide. 


  Fdenn AT cranel DOT com