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October 02, 2011


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Great article Chad. Thanks as always for the great in-depth info.


Anyway you can go into exactly what "EMC approaches for space reclaim on the device-wide level on demand" entails, please?

Is it just moving data to new luns and destroying old luns with wasted space?


Thank god for zero page reclaim in the meanwhile..

Any update on this? Are we going to see this feature enabled for array's that have a page size large enough to not overwhelm the backend?


Wow.. The entire wolrd revolves around EMC? 3PAR can do this anyway. Without VAAI. 3PARs zero detect technology works independently of this bug er feature.


If it isn't a zero detect solution then 3PAR will use the T10 unpmap to handle this. EMC sdoes this in software. So maybe they need to rewrite some code. 3PAR does it in hardware... :)

Chad Sakac

@JustOne - most array vendors have a model now where space reclaim can be done in the array itself for the devices, and that can be done here (certainly EMC platforms have mechanisms to non-disruptively do space reclaim).

The core issue is how the T10 unmap is currently implemented in some cases triggering the svmotion to fail (due to time to complete - that's on the array side, and because there is a time limit on the file disappearing - which isn't the case in other use cases, and in other host types).

IMO - the "hardware vs software" debate is pretty darn old. The only people defending ASICs furiously are those who depend on them :-)

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