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March 31st, 2015 18:00
When creating an Access Group for DDBoost over FC, what is the best practice for the device count?
When you create access groups you have to select the number of devices to create.
How to calculate it?
I know ther is a formula for the entire DataDomain:
Device Set Count
The forumla for this value is:
Let J be the maximum number of simultaneous jobs running using DFC, to the Data Domain System at any given time.
Let C be the maximum number of connections per job: 3 for Data Domain Extended Retention Systems, 1 for other types Data Domain systems
The formula
Maximum simultaneous connections to the DD system, using DFC, from ALL media servers:
S = J * C
DFC Device Count D = maximum(64, 2*(S/128)), round up
All DFC access groups must be configured with “D” devices.
In the help:
Devices: The number of DD Boost devices to be used by the group, which determines which devices the initiator can discover and, therefore, the amount of I/O paths to the Data Domain system. The default is one, the minimum is one, and the maximum is 64.
If you are working with Linux clients, you do not need to change the default. If you are working with Windows clients see the EMC Data Domain Boost for OpenStorage Administration Guide for the recommended value.
But what about the access group device count best practice for Linux, Solaris, Windows etc.?
For example if I set 4 devices, that mean that I could do 4 streams with DDBoost?
tsavgwl
7 Posts
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April 2nd, 2015 13:00
Alvaro,
I believe the best practice for Linux is to leave device count as default as you noted from the help file above, Solaris does not currently support DFC that I'm aware of and with Windows it is best determined by reviewing the following:
docu50024_Data-Domain-Boost-for-OpenStorage-2.6-Administration-Guide-.pdf. The Sizing DD Boost-over FC Device-Set section begins on page #86. I agree that the calculation is pretty intense. Here is an example from the documentation:
Assume:
-2 physical paths between the media server and Data Domain system, 50 maximum
jobs, single Data Domain system
-In this case, X=18, P = 2, J = 40, C = 1
-Maximum simultaneous connections from media server S = (J * C) = 40
-DFC device count D = max(40/2, 18) = 20
So, the Data Domain system should be configured to advertise 20 devices to each initiator on the media server.
Note that since the value of D (20) is greater than the value of X (18), it is sufficient to configure two devices only for the DFC access group with Windows clients.
As far as streams counts are concerned that is a different beast all together. The DFC device count is referring to I/O paths not NetWorker streams. Review the administration manual for your NetWorker version to determine best practice for session counts on your devices.
Hope this helps,
Tim.