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About acp_wp or acp_disk mode and the skew value
As we know the acp_wp and acp_disk mode is the secondary srdf mode,SRDF-S and SRDF-Semi is the primary srdf mode.
Q1:Does it mean if i need to set the DG to acp mode,we have to set it to SRDF-S or SRDF-Semi mode first then set it to acp mode ?
Q2: I think only when the skew value was defined while setting a device group to acp_disk or acp_wp mode, should the SRDF mode would switch between SRDF primary mode and acp_wp or acp_disk mode according to whether the invalids tracks is larger than the skew value. In this situation i should first set the device group to SRDF-S OR SRDF-Semi mode and then change the DG to acp_wp or acp_disk mode. Am i right?
Q3: When skew is defined, there exists secondary srdf mode and primary srdf mode. For example if a set a device group to acp_disk mode without giving the skew value, the device group's mode will never change to SRDF-S or SRDF-Semi unless i manually set it to these modes. Is that right?
Q4: If i want to set a device group to acp_wp or acp_disk mode, How can i decide whether to use the skew value ?
Q1:Does it mean if i need to set the DG to acp mode,we have to set it to SRDF-S or SRDF-Semi mode first then set it to acp mode ?
Q2: I think only when the skew value was defined while setting a device group to acp_disk or acp_wp mode, should the SRDF mode would switch between SRDF primary mode and acp_wp or acp_disk mode according to whether the invalids tracks is larger than the skew value. In this situation i should first set the device group to SRDF-S OR SRDF-Semi mode and then change the DG to acp_wp or acp_disk mode. Am i right?
Q3: When skew is defined, there exists secondary srdf mode and primary srdf mode. For example if a set a device group to acp_disk mode without giving the skew value, the device group's mode will never change to SRDF-S or SRDF-Semi unless i manually set it to these modes. Is that right?
Q4: If i want to set a device group to acp_wp or acp_disk mode, How can i decide whether to use the skew value ?
Anonymous
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May 31st, 2007 09:00
Leaving skew for later, the easiest method to manage this is just to set the mode you want to operate in.
If you want to run in ACP_DISK, use "symrdf -g xx set mode acp_disk".
If you want to run in Sync mode, use "symrdf -g xx set mode sync"
If the write workload is high enough that you never catch up in acp mode (and this is your primary concern), you can manually set the mode to sync. Since setting the mode to sync will have impact on your host write response times, I personally think it may be better for you to do this manually. However, you can use the "skew" value and it will toggle into and out of sync mode all by itself.
Now to try to be specific to your questions..
Q1) If you are still running code that has the choice of sync or semi-sync and you plan on using the skew value, then yes- I would first set one of these modes to establish which "primary" mode will be reverted to when you exceed the skew value.
Q2) It kinda sounds the same as Q1 - so again, if you are going to set skew value, do this to set the primary mode.
Q3) The primary mode is considered Sync or Semi-Sync. The adaptive copy is considered secondary mode. The statement is true whether or not you set a skew value. It's just that by not setting the skew value, the Symmetrix will not automatically transition back to the Primary mode. So, you are correct - just picking on terminology
Q4) I would use the skew if you have some reason to run in ACP mode and have decided that you don't want do build up invalid tracks beyond some predetermined limit (the value you would set for skew) - and - it is acceptable to your application to run in sync mode whenever you get to that value.