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1 © Copyright 2012 EMC Corporation. All rights reserved. XtremIO Data Protection (XDP) Explained View this presentation in Slide Show mode.

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Presentation on theme: "1 © Copyright 2012 EMC Corporation. All rights reserved. XtremIO Data Protection (XDP) Explained View this presentation in Slide Show mode."— Presentation transcript:

1 1 © Copyright 2012 EMC Corporation. All rights reserved. XtremIO Data Protection (XDP) Explained View this presentation in Slide Show mode

2 2 © Copyright 2012 EMC Corporation. All rights reserved. XDP Benefits  Combines the best traits of traditional RAID with none of its drawbacks  Ultra-low 8% fixed capacity overhead  No RAID levels, stripe sizes, chunk sizes, etc.  High levels of data protection –Sustains up to two simultaneous failures per DAE * –Multiple consecutive failures (with adequate free capacity)  “Hot Space” - spare capacity is distributed (no hot spares)  Rapid rebuild times  Superior flash endurance  Predictable, consistent, sub-millisecond performance *v2.2 encodes data for N+2 redundancy and supports a single rebuild per DAE. A future XIOS release will add double concurrent rebuild support.

3 3 © Copyright 2012 EMC Corporation. All rights reserved. XDP Stripe – Logical View P Q 2 Parity columns P – is a column that contains parity per row P1 P2 P3 P4 P5 P6 Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q – is a column that contains parity per diagonal. C1C2C3C4C5C6C7 4K Every block in the XDP stripe is 4KB in size. 7 Data columns 6 Data rows The following slides show a simplified example of XDP. In reality, XDP uses a (23+2) x 28 stripe.

4 4 © Copyright 2012 EMC Corporation. All rights reserved. Physical View PQ C1C2C3C4C5 C6C7 Stripe’s columns are randomly distributed across the SSDs to avoid hot spots and congestion Each SSD contains the same numbers of P and Q columns Although each column is represented in this diagram as a logical block, C The system has the ability to read or write in granularity of 4KB or less

5 5 © Copyright 2012 EMC Corporation. All rights reserved. P Q C1C2C3C4C5 C6C7 SSD Failure PQ C1C2C3C4C5 C6C7 If the SSD where C1 is stored has failed, let’s see how XDP efficiently recovers the stripe Number of Writes Number of Reads XDP always reads the first two rows in a stripe and recovers C1’s blocks using row parity stored at P Next, XDP recovers data using the diagonal parity Q. It first reads the parity information from row Q The data is recovered, using the Q parity and data blocks from C2 and C3 that are already in the Storage Controller memory Remaining data blocks are recovered using the diagonal parity, blocks previously read and stored in the controller memory, along with minimal reads from SSD 18 The system reads the rest of the diagonal data (columns C5, C6 and C7), and computes the value of C Expedited recovery process completes with fewer reads and parity compute cycles. XDP minimizes reads required to recover data by 25% (30 vs. 42) increasing rebuild performance compared with traditional RAID. Controller Memory P

6 6 © Copyright 2012 EMC Corporation. All rights reserved. Allows SSDs to fail-in-place XDP Rebuilds & Hot Space  Rapid rebuilds  No performance impact after rebuild completes for up to five failed SSDs per X-Brick 3 failed SSDs ~330K IOPS 4 failed SSDs ~330K IOPS 5 failed SSDs ~330K IOPS

7 7 © Copyright 2012 EMC Corporation. All rights reserved. Stripe number S9 S8 S7 S6 S5 S4 S3 S2 S1 Stripe update at 80% utilization % Free Blocks Stripe Number % Free Blocks S90% S80% S20% S620% S520% S120% S740% S440% S340% Diagram shows an array that is 80% full The system ranks stripes according to utilization level Always writes to the stripe that is most free Writes to SSD as soon as enough blocks arrive to fill the entire emptiest stripe in the system (in this example 17 blocks are required) Example shows new I/Os overwriting addresses with existing data – there is no net increase in capacity consumed (space frees up in other stripes) At least one stripe is guaranteed to be 40% empty => hosts benefit from the performance of a 40% empty array vs. a 20% empty array Re-ranking stripes according to % of free blocks Subsequent updates are performed using this algorithm 40% 20% 0% 40% 20% 40% 0% 40% Stripe Number % Free Blocks S30% S80% S20% S620% S520% S120% S940% S740% S440%

8 8 © Copyright 2012 EMC Corporation. All rights reserved. XDP Stripe - the Real Numbers Number of 4KB data blocks in a stripe Amount of data in a stripe Amount of Parity blocks in a stripe Total number of blocks in a stripe Total number of stripes in one X-Brick 28 X 23 = 6444KB X 644= 2576KB = = TB per X- Brick/2,024KB ≈ 3M stripes RAID Overhead (of P,Q) = 57/701 = 8% P Q Parity 28 data rows 23 data columns 25 SSDs

9 9 © Copyright 2012 EMC Corporation. All rights reserved. Update Overhead Compared RAID SchemeReads per Update Writes per Update Capacity Overhead RAID-522N + 1 RAID-633N + 2 RAID-102N × 2 XtremIO (at 80%)1.22 N + 2 XtremIO (at 90%)1.44 N + 2


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