1. XtremIO Data Protection (XDP) Explained
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2. 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. XDP Stripe – Logical View
2 Parity columns C1 C2 C3 C4 C5 C6 C7 P Q
6 Data rows P1 Q1
P – is a column that contains parity per row
The following slides show a simplified example of XDP. In reality, XDP uses a (23+2) x 28 stripe.
Q – is a column that contains parity per diagonal. P2 Q2 P3 Q3 P4 Q4 P5 Q5 P6 Q6
XDP strip here is reduced in size, this is to simplify the explanations of the XDP technology Q7 4K
7 Data columns
Every block in the XDP stripe is 4KB in size.

4. Each SSD contains the same numbers of P and Q columns
Physical View
Although each column is represented in this diagram as a logical block,
The system has the ability to read or write in granularity of 4KB or less C1 C2 C3 C4 C5 C6 C7 P Q C
Each SSD contains the same numbers of P and Q columns
Stripe’s columns are randomly distributed across the SSDs to avoid hot spots and congestion

5. SSD Failure
Remaining data blocks are recovered using the diagonal parity, blocks previously read and stored in the controller memory, along with minimal reads from SSD
XDP always reads the first two rows in a stripe and recovers C1’s blocks using row parity stored at P
If the SSD where C1 is stored has failed, let’s see how XDP efficiently recovers the stripe
The data is recovered, using the Q parity and data blocks from C2 and C3 that are already in the Storage Controller memory
XDP minimizes reads required to recover data by 25% (30 vs. 42) increasing rebuild performance compared with traditional RAID.
The system reads the rest of the diagonal data (columns C5, C6 and C7), and computes the value of C1
Next, XDP recovers data using the diagonal parity Q. It first reads the parity information from row Q
Expedited recovery process completes with fewer reads and parity compute cycles. C1 C2 C3 C4 C5 C6 C7 P Q
Controller Memory C1 C2 C3 C4 C5 C6 C7 P P Q
The C1 column will be placed at a spare capacity in the system.
Note: this slide presents the XDP capabilities, not all of those capabilities will be available at first GA (but are planned for future release).
Number of Writes
Number of Reads 6 5 2 1 4 3 15 14 7 30 22 23 24 19 18 26 27

6. XDP Rebuilds & Hot Space
Allows SSDs to fail-in-place
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. Stripe update at 80% utilization
% Free Blocks
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
Diagram shows an array that is 80% full
Stripe number S9 S8 S7 S6 S5 S4 S3 S2 S1
40% 0% 0%
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)
40%
Stripe Number
% Free Blocks S3 0% S8 S2 S6
20% S5 S1 S9
40% S7 S4
Stripe Number
% Free Blocks S9 0% S8 S2 S6
20% S5 S1 S7
40% S4 S3
20%
20%
40%
40% 0% 0%
20%

8. 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 = 644
4KB X 644= 2576KB
= 57
= 701
7.5TB per X-Brick/2,024KB ≈ 3M stripes
23 data columns
Parity P Q
RAID Overhead (of P,Q) = 57/701 = 8%
The previous slides used an XDP stripe that is based on 7 x 6 data blocks, in reality the system uses 28 X 23 data blocks
28 data rows
25 SSDs

9. Update Overhead Compared
RAID Scheme
Reads per Update
Writes per Update
Capacity Overhead
RAID-5 2
N + 1
RAID-6 3
N + 2
RAID-1
N × 2
XtremIO (at 80%)
1.22
XtremIO (at 90%)
1.44