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RAID TechnologyRAID Technology
Metadata - Disk Data Format (DDF)
• DDF - Common RAID Disk Data Format Specification developed by the SNIA Common RAID Disk Data Format Technical Working Group
• Specification defines standard data structure describing how data is formatted across disks in a RAID group
• Common RAID DDF structure allows a basic level of interoperability, such as data-in-place migration, between different suppliers of RAID technology
• Adaptec implementation of DDF is AMF – Adaptec Metadata Format
• AMF provides the space to expand metadata for new features and array types like RAID 6
LBA 0
User Data Run timeWorkspace
ConfigurationMetadata
64MB 32MB
• AMF uses more space than previous metadata formats and is at the opposite ‘end’ of the disk occupying the largest block addresses instead of the smallest
• Although it uses more space, ARC truncates available disk space to the highest 100 MB multiple that fits within the physical size of the drive, so there may not be a difference
• AMF metadata resides in the last 96MB of the disk It starts at LBA (capacity - 96MB - 1) and ends at LBA (capacity - 1)
Metadata - Adaptec Metadata Format (AMF)
No RAID
• Contiguous Data • No Fault Tolerance• Minimum 1 Drive
• Storage with no RAID logic is often referred to as Volume or JBOD
• Groups of disks known as Disk Array
HDD 1
I
J
K
L
E
F
G
H
A
B
C
D
M
N
O
P
HDD 2 HDD 3 HDD 4
No RAID
• Contiguous Data • No Fault Tolerance• Minimum 1 Drive
• Storage with no RAID logic is often referred to as Volume or JBOD
HDD 1
I
J
K
L
E
F
G
H
A
B
C
D
M
N
O
P
HDD 2 HDD 3 HDD 4
All data is lost because there is no redundancy!!
RAID 0
• Block Striping • No Fault Tolerance• Minimum 2 Drives
• RAID 0 spreads data across several drives for speed using block level striping
• High Read and Write performance
HDD 1
C
G
K
O
B
F
J
N
A
E
I
M
D
H
L
P
HDD 2 HDD 3 HDD 4
Stripe
RAID 0
• Block Striping • No Fault Tolerance• Minimum 2 Drives
• RAID 0 spreads data across several drives for speed using block level striping
• High Read and Write performance
HDD 1 HDD 2 HDD 3 HDD 4
All data is lost because there is no redundancy!!
C
G
K
O
B
F
J
N
A
E
I
M
D
H
L
PStripe
RAID 1
• Mirroring• No Striping• 100% Redundancy• 50% Capacity Loss• Requires 2 Drives
• Writes all data to both drives in the mirrored pair
A
B
C
D
A
B
C
D
HDD 1 HDD 2
Mirror Drive
RAID 1
• Mirroring• No Striping• 100% Redundancy• 50% Capacity Loss• Requires 2 Drives
• Writes all data to both drives in the mirrored pair
A
B
C
D
A
B
C
D
HDD 1 HDD 2
Mirror DriveNo data was lost because of the mirrored drive!
RAID 10
• Striped array of mirrors• Minimum 4 Drives• 50% Capacity Loss• Good write performance
• Can survive a disk failure in both mirror sets• High I/O rates achieved due to multiple
stripe segments
HDD 1
B
D
F
H
A
C
E
G
A
C
E
G
B
D
F
H
HDD 2 HDD 3 HDD 4
RAID 10
• Striped array of mirrors• Minimum 4 Drives• 50% Capacity Loss• Good write performance
• Can survive a disk failure in both mirror sets• High I/O rates achieved due to multiple
stripe segments
HDD 1
B
D
F
H
A
C
E
G
A
C
E
G
B
D
F
H
HDD 2 HDD 3
HDD 4
Supports 2 disk failures: 1 failure per mirror set
Parity
• RAID 5 - Redundancy is achieved by the use of parity blocks
• If a single drive in the array fails, data blocks and a parity block from the working drives can be combined to reconstruct the missing data
• Exclusive-OR (XOR) is the logical operation used to generate parity
• XOR compares every two bits− If the two bits are the same then an even XOR parity bit (0) is generated
− If the bits are different then an odd parity bit (1) is created
XOR
• Exclusive OR• Logical operation that generates parity for every 2 data
bits
0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 0Data Byte
Parity Byte
Data Byte
1 1 0 0 0 1 0 1
RAID 5
• Block Striping• Distributed Parity• 100% Redundancy• Better use of capacity than
RAID 1
Parity is distributed to reduce a single drive bottleneck
• Data is striped and includes parity protection
• Parity is also striped for higher performance
HDD 1
C
Parity
H
K
B
E
Parity
J
A
D
G
Parity
Parity
F
I
L
HDD 2 HDD 3 HDD 4
Stripe
RAID 5
• Block Striping• Distributed Parity• 100% Redundancy• Better use of capacity than
RAID 1
• Data is striped and includes parity protection
• Parity is also striped for higher performance
HDD 1
C
Parity
H
K
B
E
Parity
J
A
D
G
Parity
Parity
F
I
L
HDD 2 HDD 3 HDD 4
Stripe
No data is lost because of the distributed parity!
RAID 50
• Striped array of RAID 5 arrays• Minimum 6 Drives
• Can survive a disk failure in each sub-array• Data and parity striped across RAID 5 arrays
HDD 1
BParity
I
N
A
EParity
M
HDD 2
Parity
F
JParity
HDD 3 HDD 4
DParity
K
P
C
GParity
O
HDD 5
Parity
H
LParity
HDD 6
RAID 50
• Striped array of RAID 5 arrays• Minimum 6 Drives
• Can survive a disk failure in each sub-array• Data and parity striped across RAID 5 arrays
HDD 1
BParity
I
N
A
EParity
M
HDD 2
Parity
F
JParity
HDD 3 HDD 4
DParity
K
P
C
GParity
O
HDD 5
Parity
H
LParity
HDD 6
Supports 2 disk failures: 1 failure per RAID 5 sub-array
Advanced Data Protection SuiteAdvanced Data Protection Suite
Adaptec sets the RAID Feature Standard
Industry Standard RAID Features
• RAID 0, 1, 10, 5, 50, JBOD• Online Array Optimizations
− Online Capacity Expansion− RAID Level Migration− Stripe Size Configuration
• Large Array Size• Configurable Hot Spares• Hot Swap Disk Support• Flexible Initialization Schemes• Multiple arrays on a single set of drives
Adaptec Unique Features
• Optimized Disk Utilization• Hot Space (RAID-5EE)• Dual Drive Failure Protection (RAID-6)• Striped Mirror (RAID-1E)• Copyback Hot Spare
• Striping, Mirroring, Rotating Parity
• Add a drive or expand an array• Optimize for protection, capacity, or performance• Optimize performance based on data access patterns• Seamlessly support >2 TB arrays, up to 512 TB• Dedicated or global• Auto-rebuild after a disk failure• Instant availability, background, or clear• Stripe multiple arrays across the same physical disks
• No wasted space with different drive sizes• No more spindles sitting idle• Double the tolerance to drive failures over RAID-5• Spread a mirror across an odd number of drives• Auto-rebuild to original setup after drive replacement
Data Protection
AD
PS
Striped Mirror (RAID-1E)
• RAID level-1 Enhanced (RAID-1E) combines mirroring and data striping
• Stripes data and copies of the data across all of the drives in the array
• As with standard RAID level-1, the data is mirrored and the capacity of the logical drive is 50% of the total actual disk capacity (N/2)
• RAID 1E requires a minimum of 3 drives and supports a maximum of 16 drives
Data Protection
copy
Hot Space (RAID 5EE)
• Similar to RAID-5 but includes efficient distributed spare drive
• Extra spindle for better performance and faster rebuild times
• Stripes data and parity across all the drives in the array
• Spare drive part of the RAID-5EE array - Spare space interleaved with parity blocks
• Spare space dedicated to the array
• N+2 drives to implement – Minimum of 4 drives up to 16 drives maximum
Data Protection
Dual Drive Failure Protection (RAID-6)
• Similar to RAID 5 except it uses a second set of independently calculated and distributed parity information for additional fault tolerance
• This extra fault tolerance ensures data availability in the event of two drives failing before a drive replacement can occur (physically or through a hot spare rebuild)
• To lose access to the data, three disks would have to fail within the mean time to repair (MTTR) interval and the probability of this occurring is thousands of times less likely than simultaneous failure of both disks in a RAID 1 array
• Requires N+2 drives to implement
Data Protection
RAID 60
• Striped array of RAID 6 arrays• Minimum 8 Drives
HDD 1
AParity
Parity
N
Parity
Parity
I
M
HDD 2
B
EParity
Parity
HDD 3
Parity
F
JParity
HDD 4 HDD 5
CParity
Parity
P
Parity
Parity
K
O
HDD 6
D
GParity
Parity
HDD 7
Parity
H
LParity
HDD 8
• For use with high availability solutions• Can survive 2 disk failures in each sub-array• Data and parity striped across RAID 6 arrays
RAID 60
• Striped array of RAID 6 arrays• Minimum 8 Drives
• For use with high availability solutions• Can survive 2 disk failures in each sub-array• Data and parity striped across RAID 6 arrays
HDD 1
AParity
Parity
N
Parity
Parity
I
M
HDD 2
B
EParity
Parity
HDD 3
Parity
F
JParity
HDD 4 HDD 5
CParity
Parity
P
Parity
Parity
K
O
HDD 6
D
GParity
Parity
HDD 7
Parity
H
LParity
HDD 8
Supports 4 disk failures: 2 failures per RAID 6 sub-array
Selecting a RAID level Data Protection
RAID Level
Available Capacity
Read Performance
Write Performance Built-in Spare
Minimum Drives
Maximum Drives
Volume 100% =1 drive =1 drive No 1 32
RAID 0 100% ¨¨¨¨ ¨¨¨¨ No 2 128
RAID 1 N/2 ¨¨¨ ¨¨¨ No 2 2
RAID 1E N/2 ¨¨¨ ¨¨¨ No 3 16
RAID 5 N-1 ¨¨¨ ¨¨ No 3 16
RAID 5EE N-2 ¨¨¨ ¨¨¨ Yes 4 16
RAID 6 N-2 ¨¨¨ ¨¨ No 4 16
RAID 10 N/2 ¨¨¨¨ ¨¨¨ No 4 16
RAID 50N-1 per
member array¨¨¨ ¨¨¨ No 6 128
RAID 60N-2 per
member array¨¨¨ ¨¨ No 8 128
Advanced Data Protection Suite
Copyback Hotspare
• When a drive fails, data from the failed drive is built to the hotspare during the rebuild
• With Copyback enabled, the data is moved back to its original location after the controller detects that the failed drive has been replaced
• After the data has been copied back to the replaced drive, the hotspare becomes available again
• Concept of hotspare location
• Useful particularly if a SATA hotspare is protecting a SAS RAID array
• Copyback mode is enabled using Adaptec Storage Manager, HRConf or ARCConf
Data Protection
Advanced Data Protection Suite
RAID 5 Array
HotspareDisk Failure!
Hotspare kicks in…
New Disk Replacement
New Array Member
Copyback Process takes place…
