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satyaranjan1
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Question about XDP

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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?

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Avi3
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Re: Question about XDP

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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.

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Avi3
3 Silver

Re: Question about XDP

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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.

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Avi3
3 Silver

Re: Question about XDP

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

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khkris
2 Iron

Re: Question about XDP

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Hello Avi,

How long is the rebuild generally takes to complete ?

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Avi3
3 Silver

Re: Question about XDP

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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.

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khkris
2 Iron

Re: Question about XDP

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Could you provide any time range just for reference

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khkris
2 Iron

Re: Question about XDP

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

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Avi3
3 Silver

Re: Question about XDP

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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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Avi3
3 Silver

Re: Question about XDP

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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.

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