changing write cache

Question

Hello,

We have yet another new VNX 5700 array that was installed only three weeks ago. I have finally begun to map out lun provisioning for the new array when I noticed my read cache was not enabled. I enabled it to the 10% ratio,however, I noticed write cache(already enabled), was smaller than I thought it should be. After alloting the 10% left over, I still have available memory to add to write cache. I realized I have disable to change the value. Will this cause any issues? No luns are defined yet on this array.

Thanks!

Admingirl

admingirl · Answer

we have 366 GB of fast cache enabled. The array has 270 TB of usable space.

GearoidG · Answer

To answer this part

>I still have available memory to add to write cache. I realized I have disable to change the value. Will this cause any issues? No luns are defined yet on this array.

No it will not cause any issues, Obviously if this array was in production and you had to disable write cache that would have a heavy performance impact, but as you said if the array is still preproduction you should be fine.

Gearoid

etaljic81 · Answer

Did you install any enablers? The enablers consume memory. Since read cache is disabled it sounds like you enabled FAST Cache on the array.

admingirl · Answer

Thank you Ernes, yes fast cache is enabled.

dynamox · Answer

You are probably following this primus, but just in case here it is again: emc251589

etaljic81 · Answer

I would still recommend you assign some space to read cache even though FAST Cache is configured. Why? Well, you might not enable FAST Cache on every LUN you create on the array and you want those LUNs to have a little bit of read cache. So disable read and write cache, set the read and write cache and re-enable read/write cache.

admingirl · Answer

Many thanks Gearoid, Dynamox and Ernes!!

VNX

changing write cache

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