Transcript CAS, DAS, NAS, SAN and RAID:

Replication
Standard Disk
Mirrored Disk
1991
Remote Mirror
1994
Parity bit
A parity bit is a bit that is added to ensure that the number of
bits with value of one in a given set of bits is always
even or odd
Parity bits are used as the simplest error detecting code.
Transmission sent using even parity:
A wants to transmit:
1001
A computes parity bit value:
1^0^0^1 = 0
A adds parity bit and sends:
10010
*** TRANSMISSION ERROR ***
B receives:
11010
B computes overall parity:
1^1^0^1^0 = 1
B reports incorrect transmission after observing unexpected
odd result.
Introduction to RAID

What is RAID
Redundant Array of Inexpensive Disks
(Berkeley paper)
 Redundant Array of Independent Disks
(RAB)
 First defined in University of California
(Berkeley) paper 1987

Acronym coined
 5 levels defined (1-5)

3
RAID-0:Striping
Block 0
LUN
Block 1
0
Block 2
Block 3
I/O
Stream
Storage Array
Block 4
Block 5
Drive
Drive
Drive
Drive
STRIPE 0
Block 0
Block 1
Block 2
Block 3
STRIPE 1
Block 4
Block 5
Block 6
Block 7
Block 6
1
Block 7
2
3
4
RAID-1:Mirroring
LUN
Sector 0
Sector 1
Sector 2
0
I/O
Stream
Storage Array
Drive
Drive
Sector 0
Sector 0’
Sector 1
Sector 1’
Sector 2
Sector 2’
0
1
RAID10:Striping after Mirroring
LUN
Block 0
Block 1
0
I/O
Stream
Storage Array
Block 2
MIRROR
Block 3
MIRROR
Block 4
Drive
Drive
Drive
Drive
STRIPE 0
Block 0
Block 0’
Block 1
Block 1’
STRIPE 1
Block 2
Block 2’
Block 3
Block 3’
STRIPE 2
Block 4
Block 4’
Block 5
Block 5’
Block 5
0
1
2
3
RAID-2:Hashing
Disk 1
Disk 2
Disk 3
Disk 4
Disk 5
RAID
Controller
Hash Disk
HOST
7
RAID-3:Striping with Fixed Parity
LUN
Byte 0
Byte 1
Byte 2
0
I/O
Stream
Storage Array
Byte 3
Byte 4
Byte 5
Drive
Drive
Drive
Drive
Drive
STRIPE 0
Byte 0
Byte 1
Byte 2
Byte 3
Parity 0-3
STRIPE 1
Byte 4
Byte 5
Byte 6
Byte 7
Parity 4-7
Byte 6
1
Byte 7
2
3
4
5
RAID-4:Striping with Fixed Parity
Disk 1
Disk 2
Disk 3
Disk 4
Disk P
RAID
Controller
HOST
9
RAID-5:Striping with Distributed Parity
LUN
Block 0
Block 1
Block 2
0
I/O
Stream
Storage Processor
Block 3
Block 4
Block 5
Drive
Drive
Drive
Drive
Drive
STRIPE 0
Block 0
Block 1
Block 2
Block 3
Parity 0-3
STRIPE 1
Block 4
Block 5
Block 6
Parity 4-7
Block 7
Block 6
Block 7
1
2
3
4
5
RAID-6:Striping with Double Parity
DAS: Direct Attached Storage
DAS



Example SCSI Solution
Dedicated physical channel
Parallel transport
Examples




Parallel SCSI
ESCON
Fiber Channel Arbitrated Loop
(FC_AL)
Advantage: low protocol overhead


internal disks
LVD/SE
HVD
HOST A
Very fast: up to 320 MB/sec for SCSI
Ideal for internal storage
DAS is ill-suited to enterprise storage
connectivity:

Static configuration
Distance limitations
Topology limitations

Scalability limitations


SCSI port
SCSI port
internal disks
LVD/SE
HVD
HOST B
storage array
NAS: Network Attached Storage
NAS
storage on a
Local Area Network
 Uses standard
network and file
sharing protocols
 Communication with
a NAS device is at
the file level
Application
Application
Application
 Shared
Unix Client
Windows Client
Network
Unix Client
SAN: Storage Area Network
SAN
networked architecture that provides I/O
connectivity between hosts and storage
devices
 Communication over a SAN is at the block I/O
level
The storage network can be:
 A Fiber Channel network
 Uses a network of Fiber Channel
connectivity devices: FC Switches and
Directors
 For transport, an FC SAN uses FCP
 FCP is serial SCSI-3 over Fiber
Channel
 Or an IP network
 Uses standard LAN infrastructure:
Ethernet switches
 For transport, an IP SAN uses iSCSI
 iSCSI is serial SCSI-3 over IP

Host Computer
Host Computer
HBA or NIC
HBA or NIC
HBA or NIC
HBA or NIC
FC or IP
network
Array (eg
Symmetrix,
CLARiiON,
EVA)
Array (eg
Symmetrix,
CLARiiON,
EVA)
CAS: Content Address Storage
CAS
 Stores
fixed content
 Uses hash (MD5 or
similar) of the content to
provide access key
 Requires application
specific server to
mediate between user
and storage
 Provides for long term,
tamper evident storage
Networked Storage
SAN
NAS
CAS
Storage Area
Networks
Network-Attached
Storage
Content Addressed
Storage
Type of transport
Fiber Channel
IP
IP
IP
Type of data
Block
File
Object,
fixed content
Key requirement
Deterministic
performance
Multi-protocol
Sharing
Longevity,
integrity assurance
Typical applications OLTP, data
warehousing, ERP
Information
Lifecycle
Software and product Content
development, file
Management,
server consolidation Archive
Content is created
and actively shared
Content is fixed
and preserved