Tuning
Storage Area Networks (SANs) with Solid State Disk
Introduction
No
one will dispute the storage industry is in the midst of a
revolution. The dynamic
growth of the Internet and e-business applications have created new
challenges of how to effectively manage the growing stockpiles of
corporate information, to ensure timely access, and continuous
availability.
SANs
Today’s fundamental solution to this problem is the SAN.
What is a SAN? A SAN is a means to allow multiple servers to have direct
access to common storage devices or a storage pool.
A SAN can also be viewed as an alternative network dedicated
solely to storage resources.
SANs
reduce the burden placed on web, database, data warehouse, ERP, and
CRM applications by consolidating storage onto its own manageable
network that can be administered as a whole rather than many
disparate resources. SANs
also provide a better strategy for backup and managing heterogeneous
environments. By placing storage resources on a dedicated high-speed
network, numerous benefits can result:
- Centralized data eases movement between servers for improved
resource utilization.
- Manageability is improved as resources can be viewed as a
consolidated pool
- Efficient backup – either LAN-less or Server-less
- Improved Return On Investment (ROI)
Clearly,
Storage Area Networks (SAN) are the storage building block of the
future.
Solid
State Disks
FACTOID: Administrators will be able to support 400% more
storage in a SAN environment than current architectures.
Storage
devices commonly deployed in SANs include Cached Disk Arrays, JBOD,
Tape Drives, and Solid State Disks.
Solid State Disks play an increasingly important role in SANs
as their scalable design allows them to participate in SAN Islands
(standalone SANs) or in centralized SANs consisting of sub-SANs
(multiple SAN Islands interconnected through Director class
products). Because SSDs
can be shared by multiple heterogeneous servers, SAN Island
segments, or Clustered nodes, the opportunities to architect a SAN
around the performance and scalability of SSD’s can solve a myriad
of performance as well as performance tuning issues within the SAN
fabric. SSD storage resources can be flexibly apportioned to
different SAN needs and managed thru the SAN with standard tools.
This manageability allows the performance benefits of SSD to
be effectively directed to areas of the SAN where performance
acceleration is needed. SSDs
complement the other storage resources in the SAN by ensuring that
frequently accessed data is statistically and consistently
positioned on the fastest media available.
Even
with all the intrinsic benefits, SANs are not the cure-it-all for
all storage management headaches.
While many of the problems associated with server attached
storage are solved by SANs, they may cause a whole new spectrum of
issues. Like any new
technology, solving one set of problems tends to highlight
additional issues that need to be understood and acted upon.
Achieving
the ultimate benefits of SAN implementation requires architecting an
underlying virtualization scheme with enterprise-class features,
along with a flexible approach that scales with future needs.
The starting point for implementing a SAN is determining the
criticality of the data storage, how fast is fast enough, and to
what degree will it need to change in the future.
The more substantial the requirements, the more tightly
integrated the SAN architecture must be.
This means getting optimal performance, maximizing
utilization of the resources, providing open interfaces to a variety
of application needs, and having the widest range in scaling
performance, availability, and reliability.
Utilization and Performance
FACTOID: SANs
will enable users to use 90%+ of total
storage resources vs. as little as 40% utilization today.
The
key to configuring SANs for high performance database applications
is to avoid contention or bottlenecks.
So, when creating a SAN for high transaction-based database
environments, avoid the mistake of trying to use a single Fibre HBA
or loop to support the database.
Instead use multiple FC HBAs to spread I/O devices on
different interfaces to avoid contention. For the especially high transaction files such as redo
segments, rollback logs, swap space and other index types, these
should be isolated from the database structures since these file
types can quickly become a performance bottleneck.
Like
any other storage architecture, SANs can benefit immensely from
performance tuning. Since
a SAN is significantly more complex than a Cached Disk Array, for
example, tuning a SAN is more complex as well.
The key to tuning a SAN is attaining information on specific
areas of performance. Among
other things that you need to know to effectively tune a SAN, are
throughput rates by device, and average daily throughput (rates
typically measured in I/O’s per second in a database environment),
and average block or record size. Good SAN management software should provide all this
information. The key
metrics are block/record size and I/O’s per second.
Typically,
a SAN is optimized to move data in fairly large blocks, which
illustrates why Fibre Channel architectures were initially embraced
by video and pre-press operations.
Usage in database environments was slower in coming as the
average record size in many databases tends to be much smaller, not
uncommonly 2k blocks, which may not compare favorably with SCSI
connectivity, which is more suited to small block sizes.
This difference emphasizes the need to architect the SAN
around these variables for acceptable performance and scalability.
Another
concern in SAN implementations should be Quality of Service (QOS).
Since the SAN infrastructure shares common components
(Switches, Directors, and storage resources), a valid concern is
ensuring that high priority data requests are promptly responded to
and are not queued behind pending low-priority data requests.
This introduces the concept of developing a Hierarchical
storage model within the SAN for QOS purposes.
Once again, the Solid State Disk can be employed for the
pinnacle of performance and to ensure a statistically consistent
level of data accessibility and performance.
The
rate of change in SAN components has lead industry analysts like
Gartner to caution SAN implementers to plan for a three year
depreciation schedule for SAN componentry in part driven by changing
standards and in part by the advance of new interconnect
technologies such as Infiniband, iSCSI, and DAFS.
To take one step further, investment protection is a critical
factor in architecting a SAN, and one that should be considered when
making suitable component choices. The ideal SAN component would have a soft interface which
would allow the component to be adaptable over time to new
interconnect technologies and scale appropriately as needs change in
the future. Here again,
solid state disks deserve further investigation.
Regardless of the interconnect employed, servers cannot
approach the almost limitless capabilities of today’s SSD devices.
A server processing 10,000 I/O’s per second with a 4kb
block size is only moving 40MB/s of data – well beneath the
160MB/s capabilities of a single channel on an SSD.
Given leading SSD’s feature 8 to 16 connections, the
longevity of the SAN-based SSD should easily exceed three years as
long as its is adaptable to evolving and changing interconnectivity.
Storage
Virtualization
Virtualizing a solid state disk into the storage pool opens up some
very interesting scenarios. The
SSD becomes a strategic resource that can be directed within the
fabric to specific performance issues and seamlessly migrated
between platforms, operating systems, and applications for true
point and click performance resolution.
For example, the SSD is utilized on January 31st
to speed-up month-end closing on an NT based financial application.
On February 1st, the SSD (or a portion thereof)
can be allocated to help Engineering with a Unix based OS
conversion. This
mobility and scalability allows the organization to effectively
leverage the acquisition across a broader application spectrum and
recognize the benefits in virtually every facet of the enterprise.
Conclusion
SANs are enabling technologies that are in the adoption phase of the
technology lifecycle. The
networked capabilities of the SAN lend themselves to deploying
enabling technologies in an increasingly more powerful and
broad-based role across the organization.
The SAN challenge is to understand the data requirements and
architect and tune the SAN for maximum benefit to the enterprise.
Architecting solid state disk into the fabric is a powerful
and easily leveraged resource that can be used and quantified for
maximum Return On Investment.
About
the Author
Craig Harries has worked within the technology industry for over
twenty years for both hardware and software companies.
He has been very involved with solid state acceleration
products for eight years.
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