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DMP DSM for VCS SQL, Round Robin vs. Dynamic Least Queue Depth

Created: 15 Oct 2012 • Updated: 16 Oct 2012
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What is the recommended setting for the Load Balance Policy for a SQL environment?  Or, where can I find more information about the available settings?  Thanks!

Quick Look Solution

Explanation of DMP setting

Explanation of DMP setting should be the same, regardless of product, so here is the description from SFW 6.0 from SFW admin guide:

 

Dynamic Least Queue Depth
Selects the path with the least number of I/O requests in its queue for the
next data transfer.
For example, if you have two active paths, path A with one I/O request and
path B with none, DMP DSMs would select the path with the least number
of I/O requests in its queue, path B, for the next data transfer.
Round Robin with Subset
Uses a subset of paths, each in turn, in round-robin fashion. The user
specifies the paths for data transfer that make up the subset. The remaining
paths are in standby mode.
For example, if you have three active paths, path A, path B, and path C and
you specify the subset to contain path A and path B, then DMP DSMs would
use path A for one data transfer and then use path B for the next. Path C
is in standby mode and is used if path A or path B fails.
You may just have "Round Robin" option, rather than "Round Robin with Subset", so this will just mean DMP will use all available paths, rather than been able to choose a subset.  In SFW 6.0 there are lots of other modes as well, but this may not be available in the version you are using.
 
I woud guess that if you have some switches that are higher in performance or some switches are heavily loaded (so might be slower), then "Dynamic Least Queue Depth" should work better, but if all paths go through switches that are the same and equally loaded it probably makes no difference.
 
Mike

 

 

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mikebounds's picture
mikebounds
Trusted Advisor
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16
Oct
2012
SOLUTION

Explanation of DMP setting

Explanation of DMP setting should be the same, regardless of product, so here is the description from SFW 6.0 from SFW admin guide:

 

Dynamic Least Queue Depth
Selects the path with the least number of I/O requests in its queue for the
next data transfer.
For example, if you have two active paths, path A with one I/O request and
path B with none, DMP DSMs would select the path with the least number
of I/O requests in its queue, path B, for the next data transfer.
Round Robin with Subset
Uses a subset of paths, each in turn, in round-robin fashion. The user
specifies the paths for data transfer that make up the subset. The remaining
paths are in standby mode.
For example, if you have three active paths, path A, path B, and path C and
you specify the subset to contain path A and path B, then DMP DSMs would
use path A for one data transfer and then use path B for the next. Path C
is in standby mode and is used if path A or path B fails.
You may just have "Round Robin" option, rather than "Round Robin with Subset", so this will just mean DMP will use all available paths, rather than been able to choose a subset.  In SFW 6.0 there are lots of other modes as well, but this may not be available in the version you are using.
 
I woud guess that if you have some switches that are higher in performance or some switches are heavily loaded (so might be slower), then "Dynamic Least Queue Depth" should work better, but if all paths go through switches that are the same and equally loaded it probably makes no difference.
 
Mike

 

 

UK Symantec Consultant in VCS, GCO, SF, VVR, VxAT on Solaris, AIX, HP-ux, Linux & Windows

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16
Oct
2012

Thank you Mike.  I found the

Thank you Mike.  I found the information in the Admin guide per your suggestion.