components of a ds storage solution

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Components of a DS Storage Solution

Ryan LeonardStorage and Solutions Architect

System Storage February 2009


Agenda

Components of a DS3/4/5000 storage solution– Physical vs. logical

RAID levels



3 main physical components

Storage Server– Contains RAID controller(s)– Power supplies, fan assemblies, etc.

Expansion enclosures– Contains ESMs– Power supplies, fan assemblies, etc.

Disks– Where the data is actually stored



Storage Server Primary computational element

– Generally composed of two RAID controllers

– May be a discrete entity• DS4800, DS5000

– or integrated with disks• DS3000, DS4700

What is a RAID controller?– Handles all I/O operations to the underlying

media– Provides data protection via RAID

configuration– Basic management interface as well as

premium features The type of Storage Server determines the

product model (e.g. DS3200 or DS5300)

Cache memory

controller with RPA

Host interface

Drive interface

Cache



Expansion enclosures

Provides housing for individual disk drives

Connects to the controller via ESMs (environmental service modules)

Two major types of current expansion enclosures– SAS-based

• EXP3000 for DS3000 products

– FC-based• EXP810 / EXP5000 for DS4000 / DS5000

products



Disks

DS4000 and DS5000 supports FC and SATA disks– May be intermixed within an expansion

enclosure

DS3000 supports SAS and SATA disks– May be intermixed within an expansion

enclosure



FC? SAS? SATA? FC and SAS drives are very similar in

terms of performance and reliability SATA have larger capacities and a better

price per GB, however-– They are significantly ‘slower’ than either

FC or SATA disks– The may have a lower designed duty cycle

For database or other I/O oriented applications, SATA drives are probably not a good fit– Slower rotational speed– Higher access time– Somewhat limited command queuing

Sequential large block read performance can be similar



Logical components of a storage system Arrays and logical drives

– More commonly known as RAID sets and LUNs An array is a group of disks which are grouped

together using a distinct protection scheme– RAID 0, 1, 3, 5, 10, or 6*

– Group size may be either 30 drives for RAID 3, 5, and 6 or system max. for RAID 0 and 10

– The host/server has no knowledge of the underlying RAID configuration

A logical drive is an element of the array– A given logical drive can be from 10MB to the

entire size of the array it is contained in– You can have multiple logical drives per array– The logical drive is the entity that is mapped to a

given server– To the server, the logical drive appears as a

direct-attached SCSI disk of the size determined by the user

– Logical drives on the same array may be mapped to different servers (and have very different properties)

* RAID 6 is supported on the DS3200, DS3300, DS3400, DS4700, DS5100, and DS5300

Array of 3 drives

RAID 5, 2+P

Logical drive 1 – x GB

Logical drive 2 – x GB



RAID = Redundant Array of Inexpensive Disks Why use RAID?

– Enhanced performance– Access to data (disks are mechanical device and will fail!)

An array must have an associated RAID level– For DS3/4/5000 products

• RAID 0, 1, 3, 5, 10, 6• RAID 0 – from a single drive to all of the drives in the system• RAID 1 – two drives• RAID 3 – from 3 drives to 30 drives• RAID 5 – from 3 drives to 30 drives• RAID 10 – from 4 drives to all of the drives in the system• RAID 6 – from 5 drives to 30 drives

– Physical location of drive(s) is not relevant in the DS3/4/5000 products– Same type of drives must be in a given array (i.e. FC, SAS, SATA)

What’s the difference?



RAID 0 Simple striping Not actually redundant

– If a drive fails, there is no ability to recover the failed data Due to lack of redundancy, very infrequently used

– Temp. space Useable capacity = raw capacity

Drive 1 Drive 2 Drive 3 Drive 4 Drive 5

RAID 0 Array

File A

A1 A2 A3 A4 A5



RAID 1 Simple mirroring Only allows for 2 drives maximum Due to lack of scalability, very infrequently used

– Small write intensive items, like database log files Useable capacity = ½ raw capacity

Drive 1 Drive 2

RAID 1 Array

File A

A A’



RAID 10 Mirroring and striping For DS3/4/5000, a specialized subset of RAID 1 containing more than 2 drives Must be even number of drives Very common usage

– Typically applications that have high amounts of write activity or perform high amounts of random I/Os Useable capacity = ½ raw capacity

Drive 1 Drive 2

RAID 10 Array

File A

A1 A1’

Drive 3 Drive 4

A2 A2’



What is parity? RAID levels 3, 5, and 6 all use ‘parity’ to allow for redundancy of information

– Parity generated at the hardware level (remember RPA?) using a mathematical XOR– XOR can be generically thought of as ‘either A or B, but not both’

Consider the following (grossly simplified) example-

1 0

Block of data #1 (data A)

Block of data #2 (data B)

1

Block of data #3 (parity)



RAID 3 Striping with parity information Generally used for streaming or sequential workloads Parity is rotating Due to similarity to RAID 5, RAID 5 is typically used instead Useable capacity = (raw capacity – 1 disk for parity)


RAID 3 Array

File A

A1 A2 A3 A4 Ap



RAID 5 Striping with parity information Most widely used RAID type Parity is rotating Useable capacity = (raw capacity – 1 disk for parity)


RAID 5 Array

File A

A1 A2 A3 A4 Ap



RAID 6 Striping with parity plus an add’l separately calculated protection element (q) Generally used for environments with SATA drives Can sustain 2 drive failures in the group Parity and q value are rotating Useable capacity = (raw capacity – 2 disks for parity information)


RAID 6 Array

File A

A1 A2 A3 Ap Aq



Summary

Storage Server

Drive enclosure

DrivesArrayLogical drive

components of a ds storage solution

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