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February 7th, 2015 15:00

Question about XDP

in comparison with traditional RAID, we say XDP uses 23+2  for a capacity overhead of 8% only, However we also say that XDP cannot sustain two simultaneous Disk failures. How do we explain this to the customer ?. Also How much usable capacity does a half X -Brick ( 400Gb X 13) provide?

727 Posts

February 7th, 2015 21:00

We do maintain dual parity drives in each X-Brick, but we do not decode those two parity bits today. We therefore cannot sustain dual drive failure in the same X-Brick at the same time. However, this is a corner case and I would encourage you to read the XDP whitepaper to get all the other benefits that XDP provides today (being able to sustain multiple drive failures in the same X-Brick successively, no requirement for hot spare drives, etc).

A few things to note:

1. We can sustain multiple drive failures at the same time as long as those failing drives are in separate X-Bricks.

2. We can sustain multiple drive failures in the same X-Brick, as long as the second drive fails after the rebuild process from the first drive failure is complete (see the XDP whitepaper to find out why the rebuilt process itself will be very very fast).

3. We will be able to sustain dual drives failing in the same X-Brick at the same time in a future release. Work with your XtremIO specialist sales team to get more details.

4. I see that you are an EMC employee. This is a customer facing forum and is meant for the customers to ask questions - you have other forums to reach out to us.

727 Posts

February 7th, 2015 21:00

Also, the usable capacities of various capacity points is mentioned in the XtremIO data sheet.

178 Posts

February 9th, 2015 13:00

Hello Avi,

How long is the rebuild generally takes to complete ?

727 Posts

February 9th, 2015 20:00

It depends on the amount of user data and the application workload currently running on the array. We have improved the SSD rebuild time significantly in the 3.x releases.

178 Posts

February 10th, 2015 12:00

Could you provide any time range just for reference

727 Posts

February 10th, 2015 12:00

If two drives fail at the same time in the same X-Brick (however improbable that is) - we would be able to sustain that failure scenario in a future release. I would recommend getting a roadmap update from your account team for more details.

178 Posts

February 10th, 2015 12:00

And what is the resolution just in case 2 drive faulted at same time

727 Posts

February 10th, 2015 12:00

In most real world cases, it can be anywhere from 30 minutes to a couple of hours depending on the factors mentioned above.

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