Dell If Not Then Equallogic Architecture
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DELL
™
EquaLLogic
PS SEriES
architEcturE
WhitEPaPEr
FunDamEntaLLy
aLtEring thE EconomicS
oF SharED StoragE
introDuction 3
PS SEriES architEcturE FunDamEntaLS 3
PS Series Array 3
PS Series Group 4
Volumes 4
PS SEriES grouPS FaciLitatE StoragE managEmEnt 4
DiStributED PagE-baSED VoLumE managEmEnt 4
FaSt, SimPLE ProViSioning anD ScaLing 5
incrEaSED aVaiLabiLity 6
automatED managEmEnt 6
aDVancED FEaturES 6
LEVEragES inDuStry StanDarDS 7
aLL incLuSiVE buSinESS moDEL 8
concLuSion 8
about EquaLLogic PS SEriES arrayS by DELL 9
tabLES
TABLE 1: STORAGE EXPANSION COMPARISON 5
TABLE 2: PS SERIES ARCHITECTURE SOLVES BUSINESS PROBLEMS
FACING IT MANAGERS 8
CONTENTS
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introDuction
Consolidated storage promises many benefits: virtualization, reliability, high availability and centralized
management. Although these promises have yielded interesting technologies, they do not meet the need
today for affordable, easy-to-use products and are impractical for most environments.
To solve the business problems associated with storage configuration, scaling and management, the
EqualLogic PS Series was architected to provide a cost-effective, self-managing alternative to expensive
and complex offerings — bringing the benefits of consolidated storage to a broad range of markets.
The PS Series Architecture fundamentally alters the economic and management landscape for consolidated
storage by combining proven operating system, storage, and networking technologies with patented,
intelligent automation for a true state-of-the-art storage system.
This blend of technologies makes consolidated storage a cost-effective reality for all operating systems
and applications. The PS Series Architecture uses page-based volume management between arrays and
incorporates high-speed, standards-based technologies such as Gigabit Ethernet, iSCSI, Serial Attached
SCSI, and Serial ATA. The result is an affordable, scalable storage solution that grows easily from less than
a terabyte to more than 100 terabytes, while management stays minimal and constant.
While the industry talks about “next-generation storage,” EqualLogic PS Series is already there.
The PS Series Architecture was designed to meet several goals:
• Provide a single, shared storage service to hosts and applications
• Scale seamlessly from small to very large congurations
• Automate repetitive management tasks:
> Perform RAID configuration and sparing
> Provision new resources in the most efficient manner
> Allocate resources to meet changing workload demands
• Comply with industry standards
• Require no special host software for access and management
• Deliver uncompromised availability and serviceability
• Offer a full set of features, including capabilities that are usually available only as expensive add-ons,
like snapshot and volume replication capabilities
• Provide a cost-effective, easy-to-use replacement for direct-attached storage (DAS)
This whitepaper gives a brief overview of the technologies that make the PS Series Architecture uniquely
able to address the issues associated with consolidated storage.
PS SEriES architEcturE FunDamEntaLS
To achieve the goal of providing an affordable, self-managing consolidated storage solution, the PS Series
Architecture employs three essential elements: the PS Series array, the PS Series group and volumes.
PS Series Array
The foundation of the PS Series Architecture is a PS Series array — a high-performance block storage device
that is ideal for departmental or enterprise storage. Each array is a commonly configured fully-redundant
storage unit containing disks, multiple high-performance network interfaces, controllers with mirrored
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battery-backed caches and other advanced features. The disks in an array are automatically protected with
RAID (RAID 10, RAID 5, or RAID 50) and hot spares.
PS Series Group
A PS Series group is comprised of a single PS Series array or multiple arrays working together. The group
is seen as a single, shared storage service by application servers and administrators. When an array is
configured as a group member, its RAID-protected disk space is added to the group’s storage pool. Data and
network I/O to the group is load balanced across the group members’ resources.
Volumes
Administrators create volumes from the available space in the PS Series group storage pool. A volume
can be spread across multiple disks and multiple group members — this is done automatically by the
virtualization built into the arrays. The group exports volumes as iSCSI targets protected with security,
including authentication and authorization, for both discovery and access. Upon connection, hosts see
volumes as local disks. Volume snapshots and volume replicas can also be created from the storage pool.
PS SEriES grouPS FaciLitatE StoragE managEmEnt
Although comprised of one or more PS Series arrays, a PS Series Group appears to client servers as a
single entity that offers network storage access in block mode — a storage area network (SAN). Unlike
conventional SAN products, each group member “cooperates” with other members to automate resource
provisioning and performance optimization. This cooperation is a key element in the virtualization of not
only disk storage, but also controllers, caches, network links and management of the PS Series group.
The disk data served by a group is dispersed across the group members, with the placement continually
adjusted for optimal performance as resources are added or load changes occur. In addition, application
server network sessions are distributed across members to spread out the I/O requests.
The result is a storage system that scales linearly in all significant dimensions of storage capacity, network
bandwidth, application server request processing capacity and performance. In contrast, administration
remains stable as the group is expanded. There is no separate management of arrays and volumes, all
administration is performed at the group level.
With its ability to export many targets, a PS Series group can be used to consolidate storage for a wide
range of applications and servers, including e-mail, Web servers, database servers, and file/print without
compatibility or performance concerns and without a prohibitive increase in administrative expenses.
DiStributED PagE-baSED VoLumE managEmEnt
The RAID-protected disk space that each member contributes to the PS Series group’s virtualized storage
pool is partitioned into fixed-sized chunks of data, called pages. Each volume has a page map that allocates
and re-allocates pages to the members. A page map is shared by each member that contains a page of the
volume. Page maps are also used in the implementation of features like volume snapshots, replication, and
over-subscription (thin provisioning).
Page movement is a transactional operation between group members that helps ensure data integrity. Pages
can be moved transparently (that is, online and without blocking host access) across disks in a member and
across group members for automatic load balancing and to help ensure data availability. For example, to
eliminate a frequently-accessed data “hot spot,” the affected pages may be spread across different disks
or group members, without the need to move all the pages for an entire volume. The built-in load balancing
features use real-time and historical access trends, as well as capacity and status information, to help
continuously improve performance within individual arrays and the group as a whole.
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A look-up and transfer mechanism is used to efficiently track and process pages located on the group
members. When a PS Series group receives a client server request, it identifies the location of the data and
transfers the request to the member that contains the data. A request may be transferred one more time if
the desired data is located on another member.
The entire page lookup and transfer operation increases latency insignificantly relative to the disk access
time. In addition, the PS Series Architecture’s optimization technology continually adjusts storage placement
and network connections to optimize performance.
FaSt, SimPLE ProViSioning anD ScaLing
Using the scalability model from the PS Series Architecture, a PS Series group can scale linearly in both
capacity and performance — all while the system remains online. The model allows for multiple members in
a single group, with a controlled and efficient addition of resources as new members are added.
Individually, each member is a fully-functional, high-performance, highly-available storage array with
mirrored write-back caches and multiple storage network connections. Resources like disks, controllers,
caches, and network connections can be easily added and removed from a group with no complex
administration tasks or impact on availability.
As capacity and performance requirements increase, a group can be expanded. New members “learn”
configuration and performance information from the group — with no manual administrative intervention.
Data and application server connection load balancing occur automatically as the group scales. Data access
activity is monitored, and data and network connections are adjusted as needed automatically and online.
The scalability model allows for automated, online expansion in all storage dimensions, and the PS Series
Architecture nearly eliminates downtime caused by expanding or managing a storage system. Because
capacity can be added so easily, IT managers need to buy only the storage necessary for today’s applications,
easing budget constraints caused by excessive and superfluous purchases. Upgrades to new technologies
are done easily as different types of PS Series arrays can interoperate in the same PS Series group at the
same time.
Table 1 shows how the scalability model of the PS Series Architecture compares to traditional DAS and
SAN solutions.
Table 1: Storage Expansion Comparison
EXPANSION ACTIVITY TRADITIONAL DAS AND SAN PS SERIES ARCHITECTURE
Add storage capacity or network bandwidth Limited expansion capabilities are available Add another member to a group; data
remains available
Increase network connections Requires repetitive manual tasks Minimal administrative effort is required
Add controllers Storage must be taken offline; data is
not available Expansion occurs online; data remains available
Perform load balancing Requires repetitive manual tasks; data
may not be available
Operation is fully automated; data
remains available
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incrEaSED aVaiLabiLity
Consolidated storage increases the need for availability in the storage infrastructure. The availability model
used by the PS Series Architecture essentially eliminates single points of failure and enables an array to
survive multiple, simultaneous failures:
• Each PS Series array is composed of redundant components — disks, controllers with mirrored
write-back caches, network interfaces, power supplies, and cooling fans.
• Hot swappable hardware components help reduce downtime.
• Faults are well isolated — loss of controllers does not cause loss of RAID protection. This works for all
supported RAID types.
• Disks are automatically congured with RAID and hot spares are reserved to help ensure that no data
goes unprotected.
• Hot sparing and data recovery require no user intervention.
• Volume replication can provide site-level disaster protection.
• Group member hardware upgrades can be done while a group is online; simply add the upgraded array
to the group.
• A member can be decommissioned while a group is online; simply remove the array from the group.
In addition, when upgrading to the latest technology, IT managers often find themselves writing off
relatively new equipment because it is not compatible with new acquisitions. The PS Series Architecture
eliminates this problem by ensuring that previously-purchased hardware and advanced technologies will
remain interoperable.
automatED managEmEnt
The PS Series Architecture is designed to simplify storage management in several ways. RAID configuration
and hot sparing is automated, and dynamic storage and network I/O load balancing occur as resources and
performance metrics change. No longer must administrators manually map application data to specific
physical devices, controllers and network ports.
For example, to create a volume from a group’s storage pool, an administrator supplies only the name and
size. The group members handle all details of storage allocation and load balancing.
Because a group is seen as a single entity, an administrator has a centralized view of the storage;
management tasks remain constant, regardless of scale. A group can be managed through several
built-in mechanisms, including SNMP, serial line, telnet and Web-based user interfaces. No external
management station or management software is required, essentially eliminating the need for additional
purchases and administrator training.
In addition, a group can alert responsible individuals to management activity or problems through log files,
SNMP traps, and e-mail notification methods. Finally, data and management access is protected with
authorization and authentication mechanisms.
aDVancED FEaturES
With traditional SANs, many advanced features are typically expensive add-ons. For example, conventional
SAN solutions require server licenses or additional fees for snapshot and replication capabilities. Solutions
developed with the PS Series Architecture include these features at no extra charge.
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In addition, the PS Series Architecture’s snapshot capability exceeds the snapshot features available on
the market today. The real-time synchronization of snapshots across multiple volumes occurs without
interrupting applications. Snapshots allow administrators to perform online backups and can be scheduled
at regular time intervals. If data loss occurs, archived information can be rapidly retrieved to restore data
and return to normal operations.
The storage replication capabilities provided with the PS Series Architecture also enable administrators to
replicate storage to a separate location and enhance disaster recovery procedures.
Other advanced features that are included with each PS Series array — without additional license fees or
keys — include Auto-Snapshot Manager for Windows® with Smart Copy, multi-path I/O (MPIO), pooled and
tiered storage, roles-based administration, storage virtualization, and thin provisioning. In addition, as new
features are added to the PS Series over time, customers under warranty or under a service plan are entitled
to new firmware releases free of additional charges.
LEVEragES inDuStry StanDarDS
Each PS Series array uses standard Ethernet networks and industry-standard iSCSI protocols. An array has
multiple Gigabit Ethernet network interfaces, and each interface performs at 124MB/second, full duplex.
This design lowers purchase and connection costs and — unlike Fiber Channel solutions — greatly expands
the number of administrators familiar with the technology that forms the basis of the PS Series Architecture,
thus keeping the training required to a minimum.
Any Gigabit Ethernet switch can be used with an array to support most existing storage network
infrastructures. By placing the intelligence in the storage arrays instead of the switch, management of the
SAN and storage and network load balancing occurs in an efficient and cost-effective manner.
In addition, an array includes either Serial ATA (SATA) or Serial Attached SCSI (SAS) disks — the latest
generation of disk drives — which provide enhanced performance, capacity, connectivity, and reliability. Each
drive has a dedicated 300MB/second channel into the array. The drives are hot swappable and come in a
variety of models optimized for performance and capacity. The advantages of Gigabit Ethernet, Serial Attached
SCSI, and Serial ATA are many, and their feature sets and performance are expected to continue to grow.
The PS Series Architecture also can be used with most leading operating systems, applications, and
management frameworks. Any standards-compliant iSCSI initiator can access a PS Series Group by using
software implementations included with major operating systems or by using dedicated iSCSI host bus
adapters provided by leading storage vendors. Thus, a solution is available for any environment and for
every cost or performance need.
Table 2 describes how solutions based on the PS Series Architecture compare to traditional DAS
and SAN solutions.
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DIRECT-ATTACHED
STORAGE (DAS)
TRADITIONAL STORAGE
AREA NETWORKS (SAN)
EQUALLOGIC PS
SERIES SOLUTION
Budget
• Must plan for both initial and
future growth
• Low acquisition and
management cost (for a
single server)
• Scaling results in repeated
purchases and higher
management costs
• Must plan for both initial and
future growth
• High acquisition and management
(people and tools) costs
• Scaling results in expensive
infrastructure upgrades.
• Buy only what you need now.
Can easily expand at any time
• Low acquisition and
management costs
• Low scaling costs
Resources
• Each storage component
separately deployed; not a
shared storage solution
• Dedicated
• Upgrades and maintenance cause
server and application downtime
• Poor utilization of capacity and
performance
• Shared storage solution; separate
storage network infrastructure
and tools
• Many interoperability issues
• Upgrades and maintenance cause
server and application downtime
• Good capacity utilization and
performance
• Shared storage solution; utilizes
familiar network infrastructure
and easy-to-use tools
• Complete Ethernet networking
interoperability
• Deploy storage on demand and
easily change configuration
online; upgrade and perform
maintenance online
• Automated capacity utilization
and performance optimization
People
• Each storage element is
managed individually
• Repetitive, manual management
tasks in dissimilar locations
• No specialized knowledge and
experience required
• Managed as single storage system
• Repetitive, manual
management tasks
• Highly specialized knowledge
and experience required
• Each storage element is managed
individually on a network,
regardless of scale
• Automation dramatically reduces
management time and costs
• No specialized knowledge and
experience required
Time
• Management effort grows as
number of servers grows
• Short training time
• Management effort grows slowly
as number of servers grows
• Long initial training time
• Management effort remains the
same as number of servers grows
• Short training time
Table 2: PS Series Architecture Solves Business Problems Facing IT Managers
aLL incLuSiVE buSinESS moDEL
Another unique characteristic of PS Series storage arrays is the all-inclusive features. A key reason for
consolidating storage is to make storage management easier. Other SAN vendors separately license
features — working from the assumption that SAN management capabilities are somehow optional. PS
Series arrays provide all features standard.
concLuSion – SELF-managing, aFForDabLE StoragE
By allowing arrays to work collaboratively in PS Series groups and by automating time-consuming manual
tasks, PS Series Architecture offers a fundamental change in SAN implementation and operation. The
highly virtualized PS Series Architecture is designed to significantly lower the cost of consolidated storage
without a loss of capabilities. The result is a full-featured, self-managing SAN that includes dynamic load
balancing, hot swapping, hardware redundancy, snapshots, and volume replication.
Storage acquisitions are driven by current application needs, not a prediction of future needs. The PS
Series Architecture represents a dramatic advancement in storage economics, from purchase and set up
through operation and upgrades. By eliminating the barriers to adopting consolidated storage — that is,
non-standard and expensive hardware, complex technology, and high staff skill requirements — the
PS Series Architecture provides storage solutions that can quickly grow from terabytes to hundreds of
terabytes, using existing resources and familiar skills.
about EquaLLogic PS SEriES arrayS by DELL
The PS Series Architecture is a breakthrough in the process of buying, managing, and growing SANs.
PS Series arrays provide affordable, self-managing storage solutions that use iSCSI and Serial ATA
technologies with patented PS Series intelligent automation to help dramatically reduce storage complexity
and operating costs for businesses in need of consolidated storage.
THIS WHITE PAPER IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICAL ERRORS AND TECHNICAL INACCURACIES. THE CONTENT IS PROVIDED AS IS, WITHOUT EXPRESS OR IMPLIED WARRANTIES OF ANY KIND. Dell disclaims
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©2008 Dell Inc. All rights reserved. Reproduction in any manner whatsoever without the express written permission of Dell Inc. is strictly forbidden. For more information, contact Dell. Information in this document is subject to change without notice.
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