Symmetrix - Write Pending Slots

This is true.  And beyond that, a system that regularly stays at 50% WP levels is likely to reach system WP with a bit more workload, and at that point writes will have response times of read misses at best.

Thanks for your reply. What options I have to bring down the write pending level?

Hi Joean,

Increasing the cache might be one of the options but I don't see that to be as effective in solving your problem, so, I think you would need to increase the DAs and the drives in the backend so that the work load is more distributed in nature.

Thanks,

SreeHari

Generally increasing cache won't help unless it is only a short burst.

You need to either slow the writes coming into the box, or increase the speed at which they can destage.

You can increase the destage rate by adding more drives, switching to faster drives, adding DAs, or switching to a protection method with less write overhead.

Let's say for example a given disk can destage 100 IOs/sec.

And let's say it is mirrored.

So for every 100 IOs/sec of host writes, I need at least 2 disks to keep up.

If I have 1,000 host writes per second, I would need 20 disks at least.  More disks would be OK, fewer and the WP counts would build up, eventually slowing the host to the speed of the drives.

This assumes the workload is spread over the disks evenly.

Hey Quincy,

"You can increase the destage rate by adding more drives, switching to faster drives, adding DAs, or switching to a protection method with less write overhead."

I agree with all your points, I am not sure how adding more drives would increase the destage rate...Would appreciate more insight on this to increase my knowledge...

Thanks Quincy....highly appreciated...

I have limitation on the $ as this DMX-4 will be refreshed to VMAX soon.

"switching to a protection method with less write overhead" was crossing my mind earlier, and thanks Quincy56 for the same advice.

Any oher advices?

I'm currently at 5773.175.xxx (what symcli command I can use to show complete Enginuity version)?

I'm exactly on 5773.175.122 now. Unfortunately... "You do not have access to this solution" for emc213364.

Joean, the fix mentioned in emc213364 is included in release 175 so you should have that fix installed on your system.