What happens when a thin pool reaches 100%.

Question

Just like how the heading mentions my question is how does a pool react when it reaches 100% utilization. Does the performance go down. Can a pool reach 100% utilization. In my experience I have not seen a pool go more than 92-93 % as we eventually expand the pool before it runs out of space.

Fenglin1 · Accepted Answer

When the pool is full and a host attempts to perform any write that requires a new extent to be allocated, a write error is returned to the host.

sauravrohilla · Answer

perhaps you have max oversubscription set to 100% and most of the devices are fully allocated? You are unlikely to see pool full condition in this scenerio (atleast in the initial days).

Fenglin Li has already described what happens when a pool gets full.

regards,

Saurabh

Naveen_T · Answer

So there wont be any performance issues between 90-100% pool utilization?

Naveen_T · Answer

Thank you Mrinal. It is a complicated situation as there is no FAST VP on the machine and no scope of adding more data devs. But thank you for your input. Thank you everybody.

mdani1 · Answer

Hi naveen,

Potentially there should not be performance impact in case of high pool utilization but it depends on the size of the pool also. Because when you run out of space the hosts will start throwing write error as it wont get any new extent from pool.

This is bad if happens in production pool.But if you upgrade your enginuity code to 5876 and use FASTvp also side ways you can avoid such situations.Becuase starting from Enginuity 5876, allocations can come from any pool contained within the tiers of the associated FAST VP policy .FAST VP will attempt to allocate from most appropriate tier based on FAST VP performance metrics and policies & if the pool is full , alternate pool will be choosen for allocation. So till any other pool has space your safe. But still monitoring will be always needed if you over subscribe your pools.

Regards,

Mrinal Dani

moorem10 · Answer

Mrinal,

Do you have any documentation on the feature to compensate for a pool reaching 100%. Is there some configuration required to enable that capability? I've been searching for some detailed documentation and have not found anything yet.

Thanks,

Mike Moore

codyhosterman · Answer

Depends on the application actually. In VMware environment there is a feature call Stun and Resume that we support in 5875+ that will actually pause VMs that are on a VMFS that is on a TDEV in a pool that has become full. Only VMs with offending writes will be paused though, VMs with no need for additional allocation will be unaffected. I wrote about this in my paper on Symmetrix VP and VMware. For non-VMware host applications the behavior described above is what happens. The typical recommendation is to make sure you have Unisphere alerts configured on pool usage.

http://www.emc.com/collateral/hardware/white-papers/h6813-implting-symmetrix-vrtl-prvsning-vsphere-wp.pdf

Check out page 62+ on Thin Pool Monitoring/Management if you are interested in how VMware handles this on the Symmetrix

VMAX

What happens when a thin pool reaches 100%.

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