If you do windows backups, you need to also multiply # of drives with "all
local drives" - essentially how many 'child' processes can be started by your
parent job as well. Figure - how many jobs are running at once? Each job will
get the memory allocated to it.
Buffer settings?
It will depend on your drives and configuration - the speed of your drives,
your hba and TAN infrastructure.
I had LTO2 drives, my buffer size was limited. I moved to LTO5 - I increased my
buffer values.
I have done some testing - backing up the same file with different numbers of
buffers, and be aware it can be counter intuitive - sometimes a lower number of
buffers gets you more throughput.
64K - larger number seems better.
128K - sweet spot at 64 buffers
256K - sweet spot at 96 buffers
512K - sweet spot at 16 and 64 buffers!
Best throughput at 64 X 128K buffers!
However - I write to an VTL and duplicate to tape - and the duplication process
is 'stuck' with the original buffer size - so duplicating backups written at
64K buffers is painfully slow in comparison to 256K buffers.
I am still seeking a "professional opinion" on optimal buffer size for LTO5
drives.
I have one media server I had to set to 8 X 64K buffers, to get it to slow
below 20M/Second per channel, due to slow storage - I was crushing the
application.
Here is a spreadsheet I built, my speed is mostly limited by the source storage
disks and the fiber/switch TAN
Number Size Total KB per waited/delayed KB written
Buffer Buffer Second Second buffer
8 65536 605 20,904 0 0 12,246,528 - cancelled
- too slow
16 65536 604 46,801 0 0 27,494,656 - cancelled
- too slow
32 65536 605 74,268 0 0 54,272,032
64 65536 757 73,498 25K 25K 54,272,032
96 65536 360 160,233 106 243 54,272,032
128 65536 463 120,826 48 154 54,272,032
8 131072 953 45,135 0 0 42,022,400
16 131072 683 81,455 26K 26K 54,272,032
32 131072 422 135,666 7K 7K 54,272,032
64 131072 280 205,184 55 128 54,272,032
96 131072 296 193,573 28 110 54,272,032
128 131072 358 160,427 12 41 54,272,032
8 262144 695 80,014 26K 26K 54,272,032
16 262144 336 170,204 1K 1K 54,272,032
32 262144 293 196,601 62 206 54,272,032
64 262144 298 194,335 14 38 54,272,032
96 262144 295 199,338 10 33 54,272,032
128 262144 312 182,813 1 43 54,272,032
16 524288 286 204,707 43 93 54,272,032
32 524288 293 196,913 25 86 54,272,032
64 524288 287 204,287 0 0 54,272,032
96 524288 294 194,663 1 6 54,272,032
-----Original Message-----
Message: 1
Date: Tue, 18 Oct 2011 08:49:19 -0500
From: Heathe Yeakley <hkyeakley AT gmail DOT com>
Subject: [Veritas-bu] NUMBER data buffers
To: NetBackup Mailing List <veritas-bu AT mailman.eng.auburn DOT edu>
Message-ID:
<CAAWsBU5Qdsi-Kew8fWE=K3ye+6rqn7-kXKZHbwVmqGAr-eobWw AT mail.gmail DOT
com>
Content-Type: text/plain; charset="iso-8859-1"
So I've read the tuning guide, I've played around with different options for
SIZE and NUMBER of buffers and I understand the formula of SIZE * NUMBER *
drives *MPX as it relates to shared memory.
Here's my question. Of the four parameters:
MPX level
# of drives (I have 12 drives)
NUMBER of buffers
SIZE of buffers (must be multiple of 1024 and can't exceed the block size
supported by your tape or HBA)
The NUMBER of buffers and MPX level seem to be the two variables here. I
have MPX set pretty low (2 or 3) and NUMBER of buffers set to either 16 or
32. When I multiply it all out, I get a hit on my shared memory of less than
a GB. My media servers are dedicated linux hosts that only function as media
servers and that's it. Furthermore, they each have somewhere around 35 - 50
GB of memory a piece.
With my current configuration, I'm not even scratching the surface of the
amount of shared memory that's sitting idle in my system while my backups
run at night. Is there any reason I *shouldn't*** jack the NUMBER of data
buffers up to... say... 500? 1000? I've seen some people mention that they
have the number of buffers set to 64, but can we go higher?
I've searched around to see if there's a technote on the upper limit of the
NUMBER buffers parameter. If there is such a tech note, I can't find it.
Any ideas?
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