Common Server Considerations for mySAP Sizing
Server sizing is
focused on determining not only how many servers might be required to
host a specific number of end users or batch processes, but also on how
each server is configured in terms of processors, RAM, and local disks.
Server sizing is also impacted by your unique high-availability and
disaster recovery requirements, certain HA/DR offerings are only supported by specific hardware, operating system, and database combinations.
Different form factors
and types of servers might also best serve your particular needs. For
example, many of my customers purchase only rack-mountable servers, whereas
others might prefer tower models. In the same way, some prefer dense
form factors (slim-line servers that only consume a few inches of
vertical space), but others prefer larger server footprints with
correspondingly greater capabilities (like room for more disk drives,
processors, PCI and other I/O slots, and so on). If you let your
potential hardware partners know your preferences up front, you’ll save a
lot of time when it finally comes down to identifying part numbers and
putting together pricing information.
server sizing consideration involves the operating systems supported by
the platform. If your OS standard is Linux, for example, you need to
ensure that your hardware partners know this, so that they size your
mySAP solution with Linux-compatible server platforms.
Finally, scalability of
the platform needs to be taken into account. If your SAP system’s
database server requires four processors to address your estimated peak
workload, you probably do not
want to lock yourself into a four-processor platform; a larger
eight-CPU-capable system configured for only four CPUs provides you with
in-the-box vertical scalability if you later determine you need more
processing power. The same philosophy should be applied to RAM, I/O
slots, and so on, unless you are either quite certain of your needs or
willing to risk being wrong. Beyond scalability of your database
platform, you also need to share your sizing philosophy with regard to
application servers. Do you prefer in-the-box scalability, or is your
application server strategy centered around adding additional
fully-configured servers? Like determining your OS and platform
preferences, your scalability requirements should have already been
fleshed out by this time, and shared with each hardware vendor.
Disk RAID Configurations and Features
following list identifies different RAID implementations and the
configuration options, advantages, and features of each as it relates to
RAID 1, or
mirroring. For a desired amount of disk space, you must purchase and
install twice as much disk space; 400GB of usable space requires 800GB
in raw disk space. Thus RAID 1 configurations can get expensive not only
in regard to the number of physical disk drives required, but also in
terms of the number of drive shelves and even storage cabinets needed to
house the drives. In some cases, the number of array controllers and
requisite cabling must be increased as well.
1+0, or 0+1, or 10, or striping/mirroring. Like RAID 1 mirroring, half
of the configured drives are consumed to protect the data on the other
half. Thus, the same cost structure applies here. The benefit is maximum
performance, however; both writes and reads are performed faster in
RAID 1+0 configurations than in other implementations.
5, or striping data and parity. This is usually the least expensive
method of achieving high availability within a disk subsystem. Depending
upon the implementation, a RAID 5 configuration will only lose a
fraction of otherwise usable space to parity. A couple of things are
very important, however. First of all, RAID 5 implementations will never
realize the raw performance achievable by other RAID solutions. Second,
to obtain even moderate performance, a minimum number of drives (often
referred to as spindles)
must be configured. Last of all, a RAID 5 configuration might be
limited in terms of the number of drives that can be configured versus
the high availability obtained; for a system with six drive shelves, a
RAID 5 configuration is at risk (as is any RAID configuration) if two
drives are housed in the same shelf. Thus, the value derived from the
benefit of losing only a fraction of disk space to parity might be
diluted a bit, depending upon the disk subsystem vendor’s gear and how
it implements no-single-point-of-failure disk solutions.
RAID levels, like RAID 3/5 and RAID 4. These are usually best compared
to RAID 5, where a certain quantity of raw disk space is lost to
maintain parity data. Generally, the amount of required parity data is
greater in these implementations than in RAID 5, however (or overall
performance is worse), which is one reason why they tend to be less
With the basics
behind us, let’s turn our attention to some of the disk subsystems and
drives available on the market today, and how they can impact our SAP
Commonly Deployed Disk Subsystems for SAP
subsystems are available on the market today, from popular SCSI-based
solutions, to those leveraging fibre-channel and other connectivity
fabrics. From a sizing perspective, I have found that the most important
consideration is scalability, especially in terms of in-place upgrades.
Disk subsystems are expensive, and replacing your system with a new one
is even more expensive. Money spent up front to address not only
scalability but also the ability to upgrade drives, controllers, and so
on can make incremental upgrades easier, less expensive, and helpful in
extending the life of your solution. With this in mind, take care to buy
a disk subsystem that is not at the end of its useful life cycle. And
be sure to invest in a platform that has a historical and
well-documented upgrade path—a system that allows you to replace all of
your disk drives with larger and faster drives is a good example.
Similarly, a disk subsystem that supports upgrades to its array
controllers and cache makes financial sense, too.
Like disk subsystems, a
variety of disk drives are available today, ranging in capacity, form
factor, and speed. Consider the following:
operate at 10,000RPM can boost I/O performance between 5–30% more than
their 7,200RPM counterparts, depending on their application in a
computing environment. Typically, write-intensive volumes such as
database transaction logs, temporary/sort areas, and very active, or hot, tables and indexes, benefit the most.
15,000RPM hard disk drives access data 26% faster than their 10,000RPM
counterparts. These 15K drives deliver a theoretical 50% improvement in
Input/Output Operations Per Second (IOPS) over 10K drives, and 108% over
7200RPM drives (though in reality the realized performance improvement
is much smaller). Servers with multiple drives handling large numbers of
transactions benefit most from this increased I/O performance.
The largest drives on the market today can actually hold an entire SAP database, though actually doing so is never
recommended. Why? Because individual disk drives can still move only
five to seven sustained MB per second factoring in all latencies. Thus,
as always, it’s necessary to configure multiple drives rather than
save money, I typically recommend implementing something smaller than
the largest drives available, though in today’s economy, the cost
difference between different sizes continues to decrease. A good example
today is the use of 18GB drives in database design; with 36 and in some
cases 72GB drives costing nearly the same, it simply makes no sense to
invest in smaller drives. A year from now, the same argument will be
made for 36GB drives, too, as 72 and 145GB drives continue to become
more mainstream and subsequently fall in price. If you focus on spindle
count rather than pure capacity, you’ll be in good shape when it comes
drive form factors impact sizing in that the largest and newest drives
tend to be physically larger than their more mature counterparts. So, to
take advantage of the largest drives may require sacrificing in terms
of the number of drives that can be physically installed in a particular
disk subsystem. My general recommendation is to ensure that your disk
subsystem can handle different drive sizes (for future upgrades or other
needs), and then size for the number of spindles needed (to meet your
performance goals) rather than installing the largest drives. And if a
particular drive size (like 36GB) happens to be available in two form
factors, push for the smaller form factor to make more empty drive bays
available later when you need more disk space.
One other general area is
important, too, that of using disk-based storage to house online copies
of your database. One client of mine has effectively quadrupled the amount
of disk space required to house their database volumes simply because
they maintain a number of “aged” offline copies on disk, too. Another
client eats up disk space in a similar method, by maintaining a series
of client copies. And many more refresh their supporting landscape
systems with copies of the production database on a regular basis,
consuming disk space throughout the system landscape. Don’t forget to
factor in these disk copies, if that is part of your DR, client, or
Storage Virtualization—The Latest Paradigm in Enterprise Computing for SAP
The use of disk subsystems that support Storage Virtualization, or SV,
is growing. SV allows a greater number of spindles to be configured than
competing technologies, and in doing so creates a more flexible
foundation to address both growth and changing subsystem needs. Storage
virtualization improves storage utilization by minimizing wasted space
associated with configuring lots of RAID 1 volumes, and by reducing the
disk space required to maintain parity data in RAID 5 implementations.
It also supports dynamic storage allocation and reallocation, which
again minimizes wasted space by letting you “move” or allocate storage
from static drive volumes to those volumes that are growing. Beyond
typical storage subsystems, design considerations for a virtual storage
array include the following:
There is a need to design and size a new SAN abstraction layer, referred to as a group
by a number of virtual storage vendors in the market today. This term
refers to the collection of physical disk drives that are pooled
together at a hardware level, on top of which storage LUNs are created.
It is the LUNs and not the groups that are assigned RAID levels, like
1+0 or 5. The groups merely provide a way of providing a specific number
of underlying disk spindles to a database or other set of files, or
segregating different types of I/O from one another. Especially in the
latter case, it’s common to segregate OLTP transaction loads (short
discrete transactions typical of R/3, CRM, and SRM products) from OLAP
or reporting data loads (like the transactions and queries inherent to
BW and SEM).
argument for RAID 1+0 versus RAID 5 is beginning to fall apart, as the
number of drives available to a virtual RAID 5 LUN has accelerated
throughput and I/O performance levels to those nearly equaling that
achieved by RAID 1+0 configurations. This is dependent upon a number of
factors, however, including the hardware vendor’s implementation of both
SV and RAID 5.
the striping of data that automatically occurs across a group of
drives, creating simple RAID 1 mirror pairs is no longer needed. The
minimum number of disk drives required to create a virtual array is six
or eight, so the LUN created on top of these drives benefits from both
the performance and availability inherent to multiple spindles. The real
challenge then becomes laying out disk partitions, such that the
performance requirements that need to be achieved by virtue of the role
that the partition plays can indeed be achieved without losing a lot of
disk capacity. For example, no one wants to place a 20GB SQL Transaction
Log file on a RAID 0+1 (sometimes called vRAID 1) virtual array stripe
of 36GB drives—the 108GB of usable space would be virtually wasted. So
to better use the space, multiple OS partitions might be placed on it,
like SQL Server’s TempDB, SQL Server executables, and so on.
because LUNs are no longer locked in by physical disk size boundaries,
more efficient use of expensive disk resources can be realized. For
example, in a traditional SAN configured today, it would not be uncommon
to consume a pair of 18 or 36GB drives to house something as small as
an SAP executables volume, or perhaps a MSCS quorum disk; most of this
space would simply sit idly by, never to be used. And it could not be
effectively shared with other OS partitions because of the 5–7MB
throughput limitations per spindle discussed previously. In a virtual
storage solution, though, storage can be easily customized to provide
only what is needed—the spindle counts underneath the LUNs allow this
flexibility. The resulting savings in disk space can therefore be
absolutely huge for a typical mySAP implementation of three or four
components, each with four-system landscapes.
storage arrays introduce new high-speed SAN fabrics (2 Gigabit and
faster), which need to be taken into consideration when adding a virtual
storage array to an existing SAN; they interoperate, but at the slower
traditional SAN speeds.
capacity (the SV version of “hot spare drives”) becomes more critical
as data is spread across more and more drives. Why? Because the Mean
Time Between Failure (MTBF) of a large group of drives makes it more
likely that a drive failure will occur within one of your LUNs in the
next two or three years. MTBF is described as an absolute value, of
course, but in my experience it’s more like an “average.” For instance,
if the MTBF of a particular drive is one million hours, then half of
this group will succumb to a failure before it ever reaches one million
hours of service time. In my eyes, the effective MTBF for a group of 50
drives therefore drops to only 1/25th of the rated number, or 40,000
hours in this case. Thus, the likelihood of suffering from drive
failures sooner than later is that much greater, and the need for spare
drives becomes that much more imperative.
Keeping the previously
noted design considerations in mind, sizing a virtual array is quite
similar to sizing any other disk subsystem for SAP, with the following
highest levels of disk performance are achievable, though at a price.
Thus, a disk-subsystem-focused delta TCO analysis may be required in
cases where the need for maximum disk throughput is not the primary
greatest scalability is achievable too, again with the caveat that the
cost per GB may be higher than in less scalable systems. Interestingly,
though, as a virtual array grows, its storage utilization actually
improves, paying off big dividends in terms of lower and lower costs per
storage arrays are still relatively immature and untested in the area of
SAP production environments; I have only seen four implemented to date. So for
the most risk-averse SAP implementations, this lack of maturity
constitutes a sizing factor.
Other factors can
come into play, too. The fact that the VA disk controllers are two to
six times faster than their predecessors and fibre-channel disks are
faster than their SCSI counterparts is an obvious factor. The cost of
storage administration, serviceability, multivendor hardware and
operating system support, and other positive traits will push the
adoption of storage virtualization across the enterprise, too.
Similarly, difficulty in accessing virtual storage specialists, and the
paradigm change in managing data will hinder this adoption. But I
believe the most compelling reason we will see virtual storage take off
in mySAP environments is simple—awesome performance. Review the “Virtual
Arrays vs the Competition” PowerPoint on the Planning CD for compelling
data illustrating my own findings and observations.
Operating System Factors
The capabilities of
one operating system over another often come into play when sizing an
SAP solution. At the most basic level, sizing a solution based on a
preferred OS is quite common—I’ve often been told by my customers and
prospects that a particular OS is their standard, and therefore needs to
be taken into consideration. Beyond the general OS, though, lie
differences in different versions of the same basic OS, be it Windows,
Linux, S/390, or any number of Unix flavors. The following other factors
can influence an SAP sizing:
new mySAP products is first provided on Windows-based (and to a lesser
extent, Linux-based) platforms; other OS platform support is provided as
the product matures.
processing power, or other hardware-related factors may dictate a
particular operating system. A classic example is the fact that you have
to step up to Windows 2000 Advanced Server to really take advantage of more than 2GB of RAM, regardless of how much physical RAM might actually be housed in a server.
and DR considerations will drive which OS you select for your SAP
system. Even if you are clearly in one OS vendor’s camp, your need for a
certain level of high availability may force you to purchase a
different version of an OS than you otherwise would. Case in
point—Microsoft’s Windows 2000 platform again, where server clustering
is only supported on the Advanced Server and Data Center Server editions
of the OS.
OS expertise may be a factor—as with any solution component within the
stack, access to experienced and reasonably priced technical support
staff can sway your decision to go with a particular operating system.
For example, although Windows Server 2003 (WS2003) was recently
released, it will be some time before we see it underpinning productive
SAP installations; it simply takes time for a new product to mature,
reflecting both people and product development learning curves.
Database Selection and Sizing Factors for SAP
particular SAP-supported database often comes down to two things—taking
advantage of in-house experience with a particular RDBMS, and seeking to
reduce the cost of acquiring or renewing database licenses for your SAP
implementation. One of the biggest
total cost of ownership factors for an SAP solution revolves around the
database component. Other sizing-related factors include
The OS and database (DB) are often tied together; SQL Server only runs on a few select Microsoft OS platforms, for example.
High Availability and Disaster Recovery options are often tied to a particular database.
database releases are inherently faster or more capable of performing a
particular type of operation than other database releases.
Database acquisition pricing varies widely, from free (SAPDB, for example) to quite expensive, and everything in between.
widespread adoption of certain database technologies with regard to
mySAP implementations has varied as well, though I continue to see
Oracle’s and Microsoft’s (and to a lesser extent, IBM’s) database
products dominate this market.
the RDBMS deployed, understanding how quickly your database will grow is
the biggest factor of all. Typically, I try to understand my client’s
three-year plan in this regard and size the disk subsystem with room to
consideration involves whether you plan to employ SAP’s MCOD feature.
MCOD (Multiple Components, One Database) allows you to install several mySAP
components on one physical database. For example, you can combine a
couple of R/3 4.6C instances, mySAP CRM, and SAP Workplace all in one
database. One sizing key is to combine only components that are similar
in nature—though other combinations are supported in some cases, OLAP
components should only coexist with other OLAP components (like SEM with
BW), and OLTP components should only be paired with other OLTP
components. This is because of the nature of these disparate systems;
good performance would be more difficult to achieve otherwise.
The key sizing
factor is the database server, though. A conservative approach to sizing
includes sizing the individual components separately in terms of disk
space, CPU processing power, and RAM required. To calculate total disk
space required, simply add up the requirements of each component, and
subtract 10% (which according to SAP is the typical disk space savings
realized by MCOD deployments). To calculate CPU requirements, be sure
that you capture the number of SAPS that characterizes the load of each
system, and then add these together. Do the same for memory needs, and
present your combined SAPS, disk, and RAM requirements to your hardware
vendor so that an appropriate server and disk subsystem platform can be
Finally, SAP AG requires
that you combine only production systems with production systems, test
systems with other test systems, and so on. Do not mix landscapes, as it
is not supported by SAP AG.