1. Redbooks Paper
Pallavi Galgali
Ashish Chaurasia
IBM TotalStorage SAN File System as an
Infrastructure for Multimedia Servers
Abstract
Multimedia applications that deal with high-quality video and audio files place special
demands on the file system in terms of storage and data retrieval. These applications typically
use large files, requiring greater resources from the storage system in terms of capacity and
high quality of service for retrieving those files.
Storage area networks (SANs) provide an ideal infrastructure to build a multimedia serving
environment, but require additional support layers to effectively exploit the SAN with multiple
applications in heterogeneous environments. One such layer is the file system.
IBM® TotalStorage® SAN File System simplifies file and data management in SANs by
consolidating file systems across servers on different platforms. It is highly scalable for
managing large quantities of data and supports optimized access methods for mixed file type
environments. SAN File System provides better control of your data, using policy-based
automated file placement on tiered storage.
This IBM Redpaper discusses:
How a SAN satisfies the storage hardware needs of multimedia servers
How SAN File System meets the storage, access, and management requirements for
media files
This paper is intended for storage professionals looking for ways to better implement and
manage a multimedia environment. We also provide a brief overview of the architectural
design of SAN File System. For more detailed information about SAN File System, see the
IBM Redbook IBM TotalStorage: Introducing the SAN File System, SG24-7057.
© Copyright IBM Corp. 2005. All rights reserved. ibm.com/redbooks 1

2. Characteristics of multimedia data
There are certain characteristics of media files, compared with other files. Here are the main
points of difference:
File size: Media files are generally large in size and thus require greater storage space.
Retrieval method: The file retrieval pattern of media files is always sequential.
Quality of service (QoS) demand: Let us take an example of playing a movie. Consider
that we are playing a movie on a normal desktop machine. Now, start different applications
in parallel such as e-mail, FTP, and Microsoft® PowerPoint. Try to load the system to its
maximum limit. At some point, we start seeing the jitter in our movie play. This means that
we will not be able to see the movie smoothly, which implies that the media data requests
have a specific deadline associated with them. If the system can serve the data within that
deadline, we will be able to see the movie properly or smoothly. This is called QoS, or
quality of service, demand. The periodic nature of the multimedia data necessitates QoS
guarantees in the form of guaranteed throughput and bounded latency. So, our deadline
can be expressed in terms of guaranteed throughput and bounded latency. This requires a
deterministic nature in the service that is not expected from other types of files.
Looking at this special QoS characteristic of media files, we can broadly classify file system
data into two broad categories:
Real-time (RT) data
Non-real-time (NRT) data
Files that have a QoS requirement, that is, all media files, belong to the RT data category, and
all other data that do not require any deterministic nature from the file system are NRT data.
Why SAN and SAN File System?
Let us now try to understand why we propose the SAN and SAN File System infrastructure
with multimedia servers.
Why SAN?
To answer the question of why SAN, consider the scenario in Figure 1.
2 IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers

3. Disk1
Server1
Clients
Server2
Disk2
Figure 1 No storage area network
Here, Server1 is a multimedia server or streaming server serving some clients. Server1 can
serve a maximum of 10 clients, assuring the required QoS to each one. If more client
requests come in, we need to add a new server named Server2. In addition, one needs to
copy the data that Disk1 has to Disk2. The job of copying the data and maintaining two
consistent copies is very tedious, because the media data is so large in size.
A storage area network (SAN) can give us relief from this problem. As shown in Figure 2,
Server1 and Server2 can share the data using a SAN. Therefore, using a SAN enables an
easy capacity upgrade of your environment.
S
Server1
A Clients
Disk
N Server2
Figure 2 Sharing data using a storage area network
Why SAN File System?
The current challenge with SANs is that it is very difficult to use the full potential of a SAN,
and as a SAN expands, the management becomes even harder.
IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers 3

4. In a traditional environment, each server has its own file system that must be individually
configured and managed. This means that as you scale the number of servers and file
systems, you often have to scale the administrative staff. This silo approach to file systems
also makes it difficult to set and audit enterprise-wide policies for how corporate information is
to be stored and protected. Data sharing between applications that run on different servers is
difficult. Traditional SAN infrastructures are just not very flexible, in and of themselves.
Some major file and data management issues that exist in today’s SANs include:
File tasks must be done on each server.
Difficult to migrate applications to other servers.
Application downtime is required for file system changes.
No single view or single access to files or data.
No ability to pool files based on quality of service.
Therefore, we need a file management system that exploits all the functionality provided by a
SAN and also provides an easy interface to manage the data stored in a SAN. This system
needs to resolve all concurrency-related issues for a SAN environment and provide a global
namespace that will work on multiple platforms.
IBM TotalStorage SAN File System is designed to simplify file and data management in your
storage area network by consolidating file systems across UNIX®, Microsoft Windows®, and
Linux® servers. With SAN File System, files and file systems are viewed and managed as a
centralized IT resource with a single point of administrative control. By providing a common
SAN-wide file system, SAN File System can support secure, heterogeneous data sharing and
centralized policy-based storage management in an open environment.
SAN File System is designed to help you to achieve data lifecycle management efficiencies
through policy-driven automation and tiered storage management. User-defined policies
provide the ability to better match the cost of your storage resources to the value of your data.
SAN File System is also designed as a highly scalable solution, supporting both very large
files and very large numbers of files without the limitations normally associated with Network
File System (NFS) or Common Internet File System (CIFS) implementations. The result is
reduced storage management costs, enhanced productivity, and optimized storage resource
utilization.
SAN File System has been designed to help:
Simplify file and database management and improve administrator productivity through
policy-based data management
Enhance data sharing and collaboration through a single, global namespace across
heterogeneous server platforms, with high performance and full locking support
Reduce storage needs by pooling available and temporary file space across
heterogeneous servers and storage platforms and reducing the need to maintain duplicate
data for sharing
Improve application and data availability, and lower failover costs by reducing or
eliminating application downtime for storage and data management tasks
Simplify and lower the cost of data backups through application server free backup and
leveraging built-in, file-based FlashCopy® functions
Provide an on demand storage environment for fast and simple deployment through file
level virtualization, policy-based automation, and support of open standards
4 IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers

5. SAN File System architecture
In this section, we discuss the architecture of SAN File System.
Out-of-band virtualization
SAN File System is an out-of-band virtualization implementation, where the data flow is
separated from the control flow. This is achieved by separating the data and metadata (data
about the data) into different places. Out-of-band virtualization involves moving all mapping
and locking tables to a separate server (the metadata server) that contains the metadata of
the files. In an out-of-band solution, servers (such as application servers, file servers, and so
on) request authorization to data from the metadata server, which grants it, handles locking,
and so on. After they are authorized, the servers access the data directly without any
metadata server intervention. After a server has obtained access to a file, all I/O will go
directly over the SAN to the storage devices. For many operations, the metadata server does
not even intervene. Separating the flow of control and data in this manner enables the I/O to
use the full bandwidth that a SAN provides, while control can go over a separate network or
routes in the SAN that are isolated for this purpose.
How it works
SAN File System is intended to provide a common file system specifically designed for
storage networks. A key element of its design is the way that it manages the
metadata—overall information about files, such as file location, security permissions, and
locks. In many traditional file systems, the metadata resides within individual servers, which
can create limitations in sharing and accessing data across servers or across file systems. By
managing the metadata on the storage network using a metadata server, instead of
individually within all the servers, the design of SAN File System helps move intelligence out
from individual servers to the storage network so that it can be available to any server in the
network. Figure 3 illustrates this concept.
NFS
External
CIFS Clients
IP Network for Client/Metadata Cluster Communications
Metadata
Server
Cluster
Admin
Client
AIX Solaris Windows Linux Windows
2000 Server 2003
VFS w/Cache VFS w/Cache VFS w/Cache VFS w/Cache IFS w/Cache
Metadata Metadata
Server
Store
Storage Network
Metadata
Server
Shared
Storage
Metadata Devices
Server
Multiple Storage pools
Data Store
Figure 3 SAN File System architecture
Computers that want to share data and have their storage centrally managed are all
connected to the SAN. In SAN File System terms, these are known as clients, because they
access SAN File System services; although in the enterprise context, they would most likely
IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers 5

6. be, for example, database servers, application servers, or file servers. The SAN File System
client code installed on each attached server captures file requests (such as open, close,
create, or lock) and passes this information to the metadata server, which maintains the
master catalog of file metadata, notifies the client if a file address changes in flight, handles
the file placement policies and information, and handles the locking for file sharing. After SAN
File System client software has the metadata, it accesses the file data directly over the SAN.
The SAN File System client software enables users and applications to access the global
namespace through a virtual file system (VFS) on UNIX and Linux systems and an installable
file system (IFS) on Microsoft Windows systems. This layer (VFS/IFS) is built by the operating
system (OS) vendors specifically for special-purpose or newer file systems.
Metadata servers are clustered for scalability and availability of metadata operations and are
often referred to as the metadata server cluster. In a SAN File System server cluster, there is
one master metadata server and one or more subordinate metadata servers. Each MDS runs
on a separate physical engine in the cluster. Additional metadata servers can be added as
required if the workload grows, providing solution scalability. In this manner, SAN File System
is designed to provide high-performance access to data and enable sharing across
heterogeneous application servers with full-locking and security. SAN File System is designed
to allow applications on any server within the SAN to access any file in the network. No
changes to the applications typically need to be made. Storage volumes that store SAN File
System clients’ user data (user pools) are separated from storage volumes that store
metadata (system pool), as shown at the bottom of Figure 3.
SAN File System: Right fit for multimedia servers
We now describe the different advantages of using SAN File System with multimedia servers.
Better performance with large files
SAN File System provides better performance with large size files.
To understand how, let us take an example. Suppose that a multimedia application running in
the SAN File System client wants to play a file named movie.avi, which is a large file of 3 GB
stored in SAN File System space. The following set of operations are performed:
1. The multimedia application sends the request to open the file so that it can read and play
the file.
2. The open request is passed to the SAN File System client driver.
3. The SAN File System client contacts the metadata server to get the required metadata
information for the file.
4. In response, the client gets locks and the location information of the data blocks of this file.
5. After this, the SAN File System client can continue reading the data of this file from SAN
storage without any need to contact the metadata server.
Therefore, reading large files involves less metadata operations. When an activity involves
less metadata operations, SAN File System performs better. Because of its “out-of-band”
nature, it removes all bottlenecks and gives uninterrupted access directly to data. Therefore,
SAN File System provides better performance with large size files.
Extensive caching
SAN File System does extensive caching of data, as well as metadata at the client side. It
separately maintains the metadata cache. The metadata cache is about 32 MB for 32-bit
6 IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers

7. machines and 256 MB for 64-bit machines. The data cache is maintained by the normal file
system-related operations through the virtual file system (VFS) layer.
As the metadata is cached, the client does not need to contact the metadata server for the
metadata frequently, so even if the data is not available in the data cache, it can be retrieved
very quickly because of the faster Fibre Channel infrastructure support.
Therefore, extensive caching of metadata plays an instrumental role in multimedia servers
that serve popular files where there are multiple requests for the same file, because the file
can be served from the cache itself, which cuts the delay of retrieving the data from storage
multiple times.
Prefetching (read-ahead) to meet QoS
As we discussed earlier in this paper, the access pattern for RT data is sequential. And for
sequential accesses of data, it is easier to predict the next pattern of blocks to read from disk.
So while doing the reads of the current request, a file system can use this predictable pattern,
and in background, read the next few blocks of data in parallel and put them in cache.
Therefore, if the future data block is read ahead in cache along with current request, it will
speed up the operation and help in meeting the deadline.
SAN File System implements this prefetching or read-ahead technique for sequential data
accesses. Every SAN File System client (Linux, AIX® 5L™, Microsoft Windows, and Sun™
Solaris™) implements this mechanism to get better performance while doing sequential
reads to a large file.
Data placement strategy for better throughput
SAN File System has a data placement strategy that uses a round-robin method for getting
better throughput from the storage system. Figure 4 illustrates this method.
SFS Client / Multimedia server
IP Network
1 2 3
SAN
1 2 3
MDS Cluster
Volume1 Volume2 Volume3
Figure 4 Round-robin data placement strategy
Figure 4 shows a part of a very large file represented by the blocks in pink. Each file part is
then divided into sections (three in this case), which are striped across the available storage
volumes. Therefore, while retrieving data (for example, when playing a media file), these
IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers 7

8. sections can be read concurrently to improve throughput. SAN File System does all this
transparently.
This placement strategy is called the round-robin method. This method is best suited for when
data is going to be retrieved in a parallel fashion.
Policy-based, efficient storage management
SAN File System provides efficient storage management using different policies.
Files are located in storage pools. A storage pool consists of one or more storage volumes
(LUNs). Storage administrators are able to create rules for SAN File System to determine
what storage pool is used to allocate space for a file when the file is created. The storage
administrator can use any of the file attributes (such as file name, file type, date created, user
ID or group ID, and so on) to create these rules. Through the use of the policy-based rules,
SAN File System automates the task of allocating space on the desired storage volumes.
You can implement tiered storage and hierarchical storage management (HSM) using this
feature.
To understand this further, consider the following example, illustrated in Figure 5.
movie1.avi
menu.txt
project.log
Rules for File Provisioning
*.avi, *.mp3 go into Storage Pool1
IP Network *.txt, *.doc go into Storage Pool2
*.log goes into storage Pool3
SFS Client
SAN File System
Storage Pool 1 Storage Pool 2 Storage Pool 3
Fast Medium Slow
MDS Cluster
movie1.avi menu.txt project.log
Figure 5 Policy-based storage management example
Here, we have a tiered storage system with storage pools of different performance
characteristics. Storage Pool 1 provides the best throughput. Storage Pool 2 provides
medium performance, and Storage Pool 3 is the slowest. We have a policy file that shows the
rules we have set. The rules say that all AVI and MP3 files should go in Storage Pool 1,
because these are all multimedia files and have deadlines associated with them. Therefore,
we need to give the best storage pool to these types of files. Then, all TXT and DOC files go
to Storage Pool 2 and all LOG files go to Storage Pool 3. Figure 5 shows the execution of the
policy with three example files named movie1.avi, menu.txt, and project.log.
SAN File System also provides information lifecycle management capabilities, enabling
administrators to specify how files should be automatically moved among storage pools
during their lifetime. This feature can potentially lower the overall costs of storage and improve
storage space utilization, enabling a balanced use of premium and inexpensive storage
matching the objectives of the enterprise. This feature also has the potential to reduce
8 IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers

9. manual storage administration for managing space utilization and reduce the cost of storage
management.
Therefore, this policy-based storage management can prove helpful in the task of managing
media files of large sizes according to their popularity or hit rate. You can write various rules in
the policy according to your requirements.
High availability
SAN File System has some self-healing features that make it highly available for multimedia
servers:
If one metadata server from the metadata cluster fails, SAN File System has a fail-over
mechanism with which all the responsibilities of the failed metadata server can be
transferred to another, running metadata server.
SAN File System has a volume drain feature that provides nondisruptive volume data
transfers. This technique is useful if one of the disks fails in the underlying storage and
needs to be replaced with a new one.
SAN File System also has an automatic call home reporting feature, thus if there is any
problem in the system, it automatically reports the problem to an IBM Support Engineer.
Conclusion
In this study of the requirements of multimedia data, we discussed unique characteristics of
media data and its special QoS requirements from a file system. We proposed SAN as a
hardware solution and SAN File System as a software solution on top of SAN for a typical
multimedia data center. In this proposition, we touched on SAN File System architecture, and
at the end, we described the features of SAN File System that make it a perfect fit in this
media environment. In summary, we emphasized the following features:
Better performance with large files
Extensive caching
Prefetching (read-ahead) to meet QoS
Data placement strategy for better throughput
Policy-based, efficient storage management
High availability
Another point that this paper stresses is that, along with meeting the QoS demands of media
data, SAN File System provides a complete storage management solution, taking care of the
data during its entire life cycle (generally termed information lifecycle management).
Related publications and online resources
The publications listed in this section are considered particularly suitable for a more detailed
discussion of the topics covered in this Redpaper.
IBM TotalStorage: Introducing the SAN File System, SG24-7057
http://www.redbooks.ibm.com/abstracts/sg247057.html
IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers 9

10. Introduction to Storage Area Networks, SG24-5470
http://www.redbooks.ibm.com/abstracts/sg245470.html
SAN File System product page
http://www.ibm.com/servers/storage/software/virtualization/sfs/index.html
The team that wrote this Redpaper
This Redpaper was produced by a team of specialists from around the world working at the
International Technical Support Organization, San Jose Center.
Pallavi Galgali is a Software Engineer at the IBM India Software Lab in Pune, India. Pallavi
has been involved in development and maintenance projects with products such as SAN File
System and Advanced Distributed File System. She has coauthored an IBM Redbook entitled
The IBM TotalStorage Solutions Handbook,SG24-5250, and an article on IBM
developerWorks® titled “A comparison of security subsystems on AIX, Linux, and Solaris.”
She holds a degree in Computer Engineering from Pune Institute of Computer Technology,
India. Her areas of expertise include storage networking, file systems, and device drivers.
Ashish Chaurasia is a Software Engineer at the IBM India Software Lab in Pune, India. He
has been involved in development and maintenance projects with products such as SAN File
System, Advanced Distributed File System, and Virtual Private Network. One of his articles
has also been published on developerWorks, titled “Linux network packet capturing
mechanisms.” He holds a degree in Computer Engineering from Madhav Institute of
Technology and Science, India. His area of expertise include file systems, networking,
storage, and device drivers.
Thanks to the following people for their contributions to this project:
Charlotte Brooks
International Technical Support Organization, San Jose Center
Leslie Estroff
SAN File System Product Manager
Steve Gebing
SAN File System Marketing Manager
Elizabeth Barnes
International Technical Support Organization, Austin Center
10 IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers

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12 IBM TotalStorage SAN File System as an Infrastructure for Multimedia Servers