VMAX write cach limit

Question

Is there is a limit of the write cache on the VMAXs ? if a VMAX is scalable up to 1TB usable cache size , then what is the limit for write cache ?

Quincy561 · Accepted Answer

The writable cache is usually set to 80% or 75% of usable cache. You can find the amount you have with the symcfg list -v command

AranH1 · Answer

Using the output from the symcfg list -v command as Quincy indicated you will see something like this:

symcfg –sid XXX list -v

Cache Size (Mirrored) : 172032 (MB)

# of Available Cache Slots : 2478112

Max # of System Write Pending Slots : 1490739

Max # of DA Write Pending Slots : 745369

Max # of Device Write Pending Slots : 74536

Replication Cache Usage (Percent) : 1

I take the numbers above and translate everything to GB

So the total Mirrored Cache on the array:
172032 / 1024 = 168GB

The total Usable Cache would be:
2478112 * 64 / 1024 / 1024 = 151.3GB

The total system Write Cache would be:
1490739 * 64 / 1024 / 1024 = 90.9GB

And the maximum usable Volume Write Cache would be:
74536 * 64 / 1024 / 1024 = 4.5GB

You can see from the numbers above that the Replication_Policy is set on this array so the write cache is 60% of the usable cache.

Fenglin1 · Answer

VMAX system write pending limit used to be 80% by default prior to microcode 5875. At the system level, the box will go into priority de-stage mode once the system write pending count (75% by default on 5875) is reached.

VMAX

VMAX write cach limit

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