storage
Building Highly Available
Systems: The Dell
PowerEdge Cluster SE600W
and PowerVault MD3000
By Nam Nguyen
Daniel Moges
Shabana M.
Travis vigil
G
Related Categories:
Clustering
Dell PowerEdge servers
The Dell™ PowerEdge™ Cluster SE600W is a Serial Attached SCSI
(SAS)–based cluster solution comprising Dell PowerEdge servers,
Microsoft® Windows® operating systems, and the Dell PowerVault™
MD3000 storage system. Deploying this solution enables enterprises
to achieve highly available service levels in a cost-effective way.
lobal commerce and the demand for 24/7 access
Dell PowerEdge Cluster SE600W
have made information availability vital to
Dell PowerEdge clusters are based on Microsoft Cluster
enterprise success. A lack of data access during
Service software and designed to keep applications and
maintenance, hardware or software failure, or any other
services available during any single failure within the cluster.
period of downtime can lead to decreased productivity,
When Microsoft Cluster Service detects a failure, it automati-
customer dissatisfaction, and lost revenue. As high-
cally moves cluster resources from the failed cluster node to
availability technology continues to advance, both the
a healthy one and restarts the applications. PowerEdge clus-
cost and complexity associated with clustering for avail-
ters support cluster-aware applications such as Microsoft
ability and failover have been reduced significantly,
SQL Server™, Microsoft Exchange Server, and Oracle® Database
making these configurations feasible for small businesses
with Oracle Fail Safe software.
as well as large enterprise-class data centers.
In addition to application-level availability, enterprises
For data to be continuously available, IT systems must
should consider redundancy in the server-to-storage I/O
maintain uninterrupted data access during both planned and
path. Because a failure of any component along this path
unplanned downtime. Host-based clustering, in conjunction
(such as a server, adapter, controller, cable, or disk drive)
High availability (HA)
with high availability at the storage level, can greatly enhance
jeopardizes system availability, the storage system’s ability
Microsoft Windows
Server 2003
IT service levels, and represents a crucial step toward ensur-
to maintain data access during such a failure is a key part of
ing data availability and minimizing downtime problems.
a highly available storage deployment.
Serial Attached SCSI (SAS)
Allowing multiple servers (for example, a two-node cluster)
The PowerEdge Cluster SE600W is the latest addition to
shared access to data on a single storage system helps pro-
the Dell family of feature-rich clustering solutions, and the
vide application availability even if one of the servers
first based on Serial Attached SCSI (SAS) technology. It cur-
becomes unavailable.
rently supports two-node clustering based on the compo-
Dell PowerVault storage
Direct attach storage (DAS)
Storage architecture
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for the complete category index.
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The Dell PowerEdge Cluster SE600W solution and Dell
nents shown in Figure 1. The supported PowerEdge servers
PowerVault MD3000 storage array are designed to allow
provide key high-availability features such as error-correcting
enterprises of all sizes to build highly available systems in
code memory; software or hardware RAID for the internal
a cost-effective way. Deploying this solution can help main-
drives; hot-swappable drives, power supplies, fans, and PCI
tain access to critical application data even following a hard-
slots; optional dual host bus adapters (HBAs); and optional
ware or software failure.
redundant paths to the storage systems.
DELL POWER SOLUTIONS | May 2007
Reprinted from Dell Power Solutions, May 2007. Copyright © 2007 Dell Inc. All rights reserved.
technology and offers high-availability features
Operating systems
Microsoft Windows Server 2003 and Windows Server 2003 Release 2 (R2) Enterprise
Edition and Enterprise x64 Edition
Servers
Dell PowerEdge models 1800, 1850, 2800, 2850, 6800, 6850, 1950, 2900,
2950, 2970, and 6950
Storage
Dell PowerVault MD3000
such as hot spares; hot-swappable drives,
power supplies, cooling fans, and storage controllers; redundant storage controllers; redundant back-end paths with dual-port SAS drives;
and optional premium features such as snapshots and virtual disk copy.
To appreciate the potential value of cluster-
Figure 1. Supported components for the Dell PowerEdge Cluster SE600W
ing with PowerVault MD3000 storage, enterprises should first understand the host-based
The PowerEdge Cluster SE600W offers three
component fails, I/Os are transparently
RAID method of clustering. This method uses a
rerouted to the alternate path without affect-
direct connection from a storage device to each
ing applications or clients.
server, and the RAID controller itself resides on
Fully redundant configuration: This configu-
a PCI RAID card installed in the server. In an
offers only one path from each server to the
ration provides the highest availability of
external RAID configuration, like that of the
storage (see Figure 2). If a component in one
the three configurations, incorporating two
PowerVault MD3000, the RAID controller resides
path fails, the server loses access to the
SAS 5/E HBAs and two paths from each
outside the server in the external storage
storage; when this happens, Microsoft
server to the storage (see Figure 4).
system itself.
Cluster Service moves resources from the
Administrators can configure I/Os to use
Among the issues associated with host-
affected server to the other server and
any path for load balancing. If a storage
based RAID clustering, one of the most signifi-
restarts the applications.
path fails, I/Os are transparently rerouted
cant is related to the cache and performance.
Redundant configuration with dual-port
to the alternate path without affecting
The cache is high-speed memory designed to
HBAs: This configuration provides higher
applications or clients.
reduce the time required to read or write data.
configurations:
•
•
Entry-level configuration: This configuration
•
availability than the entry-level configura-
In host-based RAID configurations, the cache
tion, incorporating two ports on each SAS
Dell PowerVault MD3000
resides on the RAID adapter card located in the
5/E HBA to create two paths from each server
The Dell PowerVault MD3000 storage array, with
server. To help ensure that in the event of a
to the storage (see Figure 3). If an HBA fails,
two high-performance, active/active external
server failure the unwritten cache data is writ-
Microsoft Cluster Service handles applica-
RAID controllers and a mirrored cache, can be a
ten to disk, vendors disable the use of the
tion migration the same way it does in the
key part of designing a cost-effective, highly
cache on RAID adapters to maintain cache
entry-level configuration. If another storage
available cluster system. It is based on SAS
coherency for the cluster. Unfortunately, doing
Dell
PowerEdge
server
LAN
HBA
Controller 1
Dell
PowerEdge
server
Dell
PowerEdge
server
HBA
HBA
Controller 2
Disk drives
Dell PowerVault MD3000
Figure 2. Entry-level Dell PowerEdge Cluster
SE600W configuration
LAN
Dell
PowerEdge
server
HBA
Controller 1
Controller 2
LAN
Dell
PowerEdge
server
HBA 1
HBA 2
Dell
PowerEdge
server
HBA 1
Controller 1
Controller 2
Disk drives
Disk drives
Dell PowerVault MD3000
Dell PowerVault MD3000
Figure 3. Redundant Dell PowerEdge Cluster
SE600W configuration with dual-port HBAs
Reprinted from Dell Power Solutions, May 2007. Copyright © 2007 Dell Inc. All rights reserved.
HBA 2
Figure 4. Fully redundant Dell PowerEdge
Cluster SE600W configuration
www.dell.com/powersolutions
71
storage
so can cause a significant degradation in cluster performance.
When using external RAID, the cache
resides on the external controller within the
storage system, and cache coherency can be
maintained without disabling the cache functionality. For this reason, external systems
are preferable for a clustered configuration.
“The PowerEdge Cluster SE600W and PowerVault
MD3000 are designed to build upon the reliability of
parallel SCSI while addressing that technology’s performance, reliability, and scalability limitations.”
Storing the cache separately from the server
helps eliminate the risks associated with a
server failure in a host-based RAID cluster.
Cluster SE600W compared with the parallel
As an external storage system, the PowerVault
SCSI–based PowerEdge Cluster SE500W.
MD3000 is ideal for highly available two-
In a PowerEdge Cluster SE500W, the write
cache is disabled in the RAID controller to maintain cache consistency, because the RAID intel-
node clustering applications on PowerEdge
Performance
ligence is part of the controller residing on the
servers when performance and access to data
The PowerVault MD3000 can provide better
host. In a PowerEdge Cluster SE600W, the write
are critical.
performance than PowerVault 22xS storage
cache is enabled in the RAID controller, because
because of its increased data transfer rate over
the RAID intelligence is part of the controller
Cluster features and advantages
the SAS link and its enabled write cache. While
residing on the external storage device. Each
The PowerEdge Cluster SE600W and PowerVault
the maximum data transfer rate for Ultra320
storage controller has 512 MB of cache, which
MD3000 are designed to build upon the reli-
SCSI is 320 Mbps (and the complications of the
helps significantly improve overall system
ability of parallel SCSI while addressing that
shared bus architecture make increased speeds
performance.
technology’s performance, reliability, and scal-
unlikely), SAS currently offers speeds of up to
ability limitations. Figure 5 summarizes the
3 Gbps, and the SCSI Trade Association plans
Reliability
cluster features of the SAS-based PowerEdge
for it to eventually support up to 12 Gbps.
When deployed in an environment using
parallel SCSI and a shared bus architecture, a
misbehaving device can bring down the entire
Dell PowerEdge Cluster SE500W
Dell PowerEdge Cluster SE600W
HBAs
Up to two PowerEdge Expandable RAID
Controller (PERC) 4/DC or PERC 4e/DC
adapters per node
Up to two SAS 5/E HBAs per node
Storage
Up to four PowerVault 22xS enclosures
One PowerVault MD3000 enclosure connected
to up to two PowerVault MD1000 enclosures
Cluster SE600W configuration provides two paths
Cables
68-pin shielded P-type SCSI cable for
connection to the host, up to 12 meters long
Compact cable and connector, up to 6 meters
long
dual-port SAS drives to allow data access from
Hard drives
13 SCSI hard drives per enclosure
15 SAS hard drives per enclosure (with
expansion to up to 45 drives by adding
PowerVault MD1000 enclosures)
As a result, if a component in a storage path fails,
system. The PowerVault MD3000 offers a pointto-point architecture in which such devices can
be easily isolated without affecting the entire
system. In addition, the fully redundant PowerEdge
from the servers to the storage, and includes
either port from one of the two storage controllers.
the multipath software can automatically reroute
the I/Os to the alternate path without affecting
Redundant path
to the storage
system
No
Yes, including redundant storage controllers
with failover capability, dual-port SAS drives,
and a multipath failover driver
RAID
RAID-1, RAID-5, RAID-10, and RAID-50
RAID-0, RAID-1, RAID-5, and RAID-10
Scalability
Write cache
Disabled in cluster mode
Enabled in cluster mode
the shared bus, while a SAS domain can sup-
Storage
manageability
Dell OpenManage Storage Services and Dell
OpenManage Array Manager, installed on a
host directly connected to the storage
Dell Modular Disk Storage Manager with
advanced features such as snapshots and
virtual disk copy, installed on a management
station (either in-band through the SAS link or
out-of-band over the network)
port up to 16,384 devices without performance
the applications or clients.
Parallel SCSI can support up to 16 devices on
degradation. The PowerEdge Cluster SE600W
can support up to 45 SAS hard drives by adding
PowerVault MD1000 disk expansion enclosures
to the PowerVault MD3000 using a daisy-chain
Figure 5. Feature comparison of Dell PowerEdge Cluster SE500W and PowerEdge Cluster SE600W
72
DELL POWER SOLUTIONS | May 2007
topology (see Figure 6).
Reprinted from Dell Power Solutions, May 2007. Copyright © 2007 Dell Inc. All rights reserved.
LAN
Dell
PowerEdge
server
HBA 1 HBA 2
Dell
PowerEdge
server
HBA 1 HBA 2
Highly available cluster solution
Daniel Moges is a systems engineer adviser in the
The Dell PowerEdge Cluster SE600W and
High-Availability Cluster Development Group at
PowerVault MD3000 take advantage of SAS
Dell. His responsibilities include developing SCSI-,
technology to offer enhanced performance, reli-
iSCSI-, and Fibre Channel–based high-availability
ability, and scalability, and include additional
clustering products; his current interests related to
features not found in parallel SCSI–based
high-availability clustering include enterprise stor-
PowerEdge Cluster SE500W configurations. This
age technologies and database systems. Daniel
cost-effective clustering solution can benefit
has a B.S. in Electrical Engineering from the
enterprises of all sizes that require high avail-
University of Illinois at Urbana-Champaign.
ability for critical applications such as dataController 1
bases, messaging systems, and file, print, and
Dell PowerVault
MD3000
Shabana M. is an engineering analyst in the High-
Web servers.
Availability Cluster Development Group at Dell.
Dell PowerVault
MD1000
Nam Nguyen is a senior consultant in the High-
and Fibre Channel–based clustering solutions and
Availability Cluster Development Group at Dell,
application performance. She has a B.E. in
Dell PowerVault
MD1000
and the lead engineer for SAS, Internet SCSI
Computer Science and Engineering.
Controller 2
Disk drives
Her interests include the development of SCSI-
Figure 6. Fully redundant Dell PowerEdge
Cluster SE600W configuration with two daisychained Dell PowerVault MD1000 enclosures
(iSCSI), and Fibre Channel Dell PowerEdge Cluster
products. His current interests include business
Travis Vigil is a senior product marketing consultant
continuity, clustering, and storage technologies.
for Dell PowerVault storage. He has a B.S. from
He has a B.S. and an M.S. in Electrical Engineering
Stanford University and an M.B.A. from Northwestern
from the University of Texas at Austin.
University’s Kellogg School of Management.
Reprinted from Dell Power Solutions, May 2007. Copyright © 2007 Dell Inc. All rights reserved.
www.dell.com/powersolutions
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