Документ взят из кэша поисковой машины. Адрес оригинального документа : http://classic.chem.msu.su/gran/gamess/guideline.doc Дата изменения: Thu May 11 23:25:26 2006 Дата индексирования: Mon Oct 1 19:48:24 2012 Кодировка:

Guideline for building and setting-up a win32x64 PC computing system
running NT-family Microsoft OS with PC GAMESS 6.x.

by Serge V. Kovrigin, IPMS & Kiev National University, ї2005


Table of Contents:

1. Conventional vs. direct methods: tasks, where usage of conventional
methods still reasonable.
2. Building a PC for PC GAMESS conventional calculations: consideration
of general aspects and desires.
3. OS and PC GAMESS tuning procedure - achieving best performance.

*This how-to doesn't claim to be an official and/or finished paper, neither
has it come from the authors of GAMESS or PC GAMESS software; hereby, you
may consider these materials as a set of recommendations, obtained as a
result of usage of PC GAMESS by experienced users. This experience now is
to your attention.

Why waste time for reading this? Authors of this how-to achieved almost
100% efficiency (means CPU time/wall-clock time ratio) and three times as
short calculation times compared to classical set-ups.

1. Conventional vs. direct methods: tasks, where their usage still
reasonable.

PC GAMESS is being continuously developed and upgraded. As a result,
in the last 6.5 build direct SCF code is almost as fast as conventional SCF
code for basis-sets of medium complexity, and even faster in certain
situations. Undoubtedly, future belongs to direct methods, due to their
excellent scalability with parallel computing, higher reliability as a
consequence of avoiding using HDD operations in most of the time and for
same reason, lower costs for building a node in a cluster or workstation.
However, at present time there are a lot of calculations, which can be
performed much faster using conventional methods.

Typically, all these calculations are similar in several aspects: these are
big systems (more than a thousand of base functions), with basis set used
up to 6-31G**. Benefit from using techniques described below should be
noticeable for any disk-intensive tasks, i.e. MP2, but it is only
estimation and was not completely tested.

The root of all problems.

To tell it simpler, with conventional methods the more 2e integrals
needed for a specific task, the wider bandwidth of HD-storage system should
be. With increasing 2e integrals quantity not only storage capacity demands
rapidly grows, but a number of integrals needed to be read/written per
second increases. At some point, HDD storage system just cannot provide
necessary throughput for PC GAMESS, and CPU has to wait for information to
be delivered. This situation can be easily observed with a Task Manager on
a P4-3GHz class PC running a 6-31G basis set job of about 800 basis
functions in size, when CPU load drops to 60%.
On the other hand, PC GAMESS doesn't operate HDD directly (as almost
any other program) but through OS. With increasing number of read/write
requests OS overload grows and more CPU time is distributed to serve those
requests. As a rule, OS use its own cache to speed-up read/write operations
(this referred to as 'read-ahead' and 'delayed-write' techniques), which in
real slows down disk operations instead of speeding them up. This happens
primarily because of OS assumption of random and repeated requests, while
PC GAMESS most of the time uses sequential access to its files. There are
some other reasons which lead to slowing everything down. Again, this can
be observed with a Task Manager, with option 'Show OS core time' set. Red
graph will show OS overhead, which for large tasks may almost be as high,
as PC GAMESS CPU load.
These main two reasons make prerequisite the development of direct
methods. But direct methods become ineffective when basis-sets used are not
too complicated. As a result, we have something-like 'death-zone' for a
range of tasks, which are too complicated for conventional methods, while
still too simple for direct methods to be used. Following materials will
show how to overcome this issue.

2. Building a PC for PC GAMESS conventional calculations.

With a wide variety of PC-based platforms and solutions on the market
it is not easy to make a universal decision. The matter of fact is,
however, that the final result and your satisfaction with your new
workstation/node is not simply a function of money you spent! The general
rule: "try". You should test given configuration with your specific tasks.
The best configuration will be the most reliable among the most fast ones.
Please remember, even if you waste a month for a testing, you will save
much more time in a real job.

Here we only point to several aspects you should keep in mind when building
your "GAMESS PC".

1. Reliability. Your hardware must be reliable enough to operate for
months without accidental reboots, errors, malfunctions. This demand
becomes even stricter, if you plan to use your PC not for calculations
only, but for office-work as well. Ideal, but expensive solution is to
use server platforms. At the same time practice shows that high-end
hardware parts for desktop PCs from brand manufacturers are good
enough to be an optimal choice for the smaller price.
2. Expandability. Pay special attention to upgrade opportunities of your
hardware: first of all it applies to memory expandability. In your
work, amount of memory will be one of the major factors of efficiency,
so you must be able to add memory as needed. Upgrading processor also
can boost performance to some extent.
3. Harmonicity. In conventional SCF calculations CPU power and HDD-
storage system capacity should be balanced for your specific tasks. It
is foolish to purchase high-end expensive processor and one-HDD
storage-system (even if it is a SCSI disk), as more likely than work
fast such system will work slower compared to not so fast processor
and a 2-disk RAID (see below).
4. Wisdom. Not all 'brand new' means perfection! Preferring new platforms
and solutions you risk wasting your time and your money for glitches
and errors. The optimum choice is chipsets of 3rd,4th. generation in a
family (for Intel, for example, 845,865,875). Remember, any technology
needs time to become reliable.

Below we consider some applied advices, but you should remember that all
depends on your specific tasks, so you should be careful and make your
tests independently.


Guidelines to building efficient and reliable PC-GAMESS computer


For all cases, amount of memory installed must overcome needed by your task
plus OS demands and even 20-25% greater for a stable and efficient working.


Platform choice and discussion.

Intel platform:

-Processor with HTT support if office-working on computer is assumed.
-System bus speed: 533, 800 (makes no difference)
-Memory (266,333,400,500) (makes no difference), 2 channel mode.
-Motherboard: supporting RAID (I865,I875)
-RAID: built-in (best ones are ICH5R, ICH6R).
-HDDs: 2xSeagate SATAII 200Mb.
-Cooler: Zalman.

AMD platform:

-AMD64 2800+-3200+.
-System Bus speed (Hyperlink) - doesn't matter, except for NVIDIA early
chipsets (150)
-Memory speed- makes no difference.
-Motherboard: supporting RAID (VIA KT880Pro, SiS)
-RAID: built-in, on a bridge, VIA (for VIA chipsets), SiS, or third party
manufacturers.
-HDDs: 2xSeagate SATAII 200Mb.
-Cooler: Zalman.

Note on platforms:

For conventional calculations the main limiting factor is HDD storage
system throughput. Thus, both processor and platform should be chosen with
keeping this detail in mind.

At present time, AMD64 3200+ and Intel P4 3200 are almost the same at
performance in PC GAMESS. AMD64 makes SCF calculations faster to up to 20%
than Intel does, while 2e integrals and 2e gradients are generally 10%
slower. Taking into account lower prices for AMD64 platforms, author would
recommend latter for conventional SCF calculations.

Note on Intel:

-HTT brings almost nothing to the speed of calculation, but it helps if you
plan to use your computer for some office works while PC GAMESS is running.
-Higher practical limit for processor speed for 2 disks RAID-system is 3,2
GHz.
-Prescott core radiate much more heat, than Northwood core, thus it is
potentially not as stable as Northwood is. No performance boost compared
to Northwood was marked.
-Best results in stability and performance were achieved on I875Chipset.

Note on AMD64:

-AMD64 2800+-3000+ is the optimum solution. AMD FXs at higher frequencies
can provide up to 30% of performance boost (for several time greater
prices). However, this performance stills generally unclaimed because of
insufficient HDD storage-systems throughput even when RAID is used.
-Low-end AMD processors, like Sempron (Paris core) is simply a cut-off from
AMD64 core: less cache (256 KB), 64-bit instructions are blocked, rating
index differs from AMD64 processors (that means that Sempron 2800+ and
AMD64 2800+ is NOT the same). However, when operating at equal core
frequencies, these two cores are very close in performance, while
considerably differs in prices. As far as 64-bit computing is not utilized
in PC GAMESS by now (as well as in popular OSs), this processor may become
your choice. Yet be aware that some of Paris dies maybe simply degraded and
burned-out AMD64 ones, so their reliability may be not enough for building
computer for PC GAMESS calculations. You should test everything carefully
before making your final choice.
-At present time, VIA solutions seems to be the most stable and productive,
with SiS next to them.

Note on Cooler:

-You are free to use one you like, but you should pay special attention to
keeping your CPU as cool as possible. Best results achieved with pure
copper coolers (like Zalman ones).


Note on RAID:

-There are several opportunities to make RAID in your system, thus
enhancing your HDD storage system throughput and overall speed of
calculations. These are:

1) software RAID
2) built-in RAID
3) PCI-card RAID from third party manufacturers.

We will not here discuss 1), since it loads CPU, crashes if OS crashes and
has some minor disadvantages. As for items 2) and 3), there is something
one must know.

Basically, the best solution now is built-in RAID. On modern motherboards,
RAID controller utilizes SATA or SATAII interfaces, and provides 2 SATA
ports. Thus, only 2 disks RAID can be made. There are some exceptions on
the market (like ICH6R on i925 chipset), which were advertised to have 4
disks RAID on-a-chip, so you should check if those are 'in-flesh' at the
moment. Unfortunaly, due to revolutionary re-designing of Intel 925 chipset
compared to preceding chipset family, this advantage of ICH6R sinks in
other disadvantages. Also, there are a lot so-called 4-port RAID on the
market, but at a closer look all these solutions are combined 2-ports on
integrated controller, and 2-ports on add-on third-party chip, and this is
the case, when 2+2 is not the same as 4. For above reasons we will discuss
only 2 disks RAIDs.

Without going into details, ICH5R is simply the best among ALL RAID
controllers (including PCI-card RAIDs). On I875 Chipset it provides up to
125Mb/sec reading and slightly less writing rates, which is simply doubling
speed of single HDD (Seagate 200 SATAII), with CPU loading less than 5%.

Then comes built-in RAID controller on VIAKT880Pro for AMD64 platform.
Results are slightly worse, but still high - 110Mb/sec.

Add-on chips from third-party manufacturers will make hardly more than 85-
90 Mb/s and the worst result shows PCI RAID cards. For latter, even
manufacturer name doesn't play any role: simple 2-port FastTrack shows the
same result as about-professional server 4-port Intel RAID card with its
own In-Out Intel 386 processor and 64Mb of buffer memory! Results are as
low as 65-70 Mb/sec.

The key for understanding this strange behavior is very simple: PC
GAMESS in the main uses sequential disk access, thus any IO processors and
buffers won't help a bit. The only thing matter here is a bandwidth of IO
channel between HDD storage-system and memory. In a built-in solutions,
like ICH5R or VIA RAID, RAID controllers are linked to memory directly
through high-speed bus, Intel hyper-link (266mb/sec) or AMD Hyper Transport
(up to 1Gb/sec), which provides bandwidth enough wide for not to delay
information being transferred from RAID controller. Thus, as soon as new
drives are available, you can replace your old ones and achieve even
greater performance rates.
When add-on chips are used on a motherboard to build a RAID,
situation is much worse, because they are linked to PCI bus, which
throughput is limited to (theoretically) 133 Mb/sec. In practice, it is
even lower because of sharing PCI bus with other devices and transferring
some subordinate service information. This situation is getting even worse
if RAID controller located on an ordinary PCI card.

Summary: very simple. Only PCI express architecture can benefit from any
add-on solutions. However, it is not stable enough, when speaking of Intel
new chipset family. Of course, you can try using server platforms, where
PCI 64 standard provides up to 512 Mb/sec capacities for PCI devices. Such
platforms are a matter of necessity for dual-CPU solutions. As for today
single-CPU computers, the choice is for built-in RAID controllers.

Note on Disks:

-You will need 2 of them. Ideal would be ones produced within one lot (with
serial numbers differs in last letter/sign). This will guarantee their
identity in main parameters: speed, access time, flash version and
lifetime. Each of those is critical for RAID stability and performance.
-You choose manufacturers to your own taste. However, you should follow
several recommendations:

. Do not choose low-end models.
. Pay attention to country of assembly - Malaysia and Singapore seems to
be more reliable.
. From HDD specification you should worry about speed of sequential
reading/writing and lifetime only.
. Remember that maximum performance in sequential operation achieved by
disk with "most Gbytes per plate".
. Buy large disks: suppose your task needs 80 GB, in that case you
should purchase not less than 160 GB disk. In the beginning of disk
reading/writing speed may differ by a factor of two! Only first 20-30%
of disk's volume is the most rapid.
. Use disks, which meet SATA-II specifications; NCQ support won't do a
thing, because it prevails only for random requests.

*Disks we a talking about are ones designed for desktop platforms. For
server platforms, where SCSI disks are traditionally used, situation may
differ to some extent, but not in general.

*Disks mentioned above meet all those requirements.

-If you plan working on computer, where PC GAMESS runs, you should also
purchase a separate disk for OS and swapping file.

-COOLING. Your disks will work without a pause for weeks or months. They
may become hot while their operation. Temperatures of above 50C are
considered to be high and may lead to premature death of your HD. Optimum
operational temperature is up to 40C. To achieve this level of
temperatures, extra HDD cooling is the matter of necessity. You may locate
powerful-enough fan (80 to 100 mm in diameter) in front of you HDDs, use
water-cooling system, or (original solution) you may attach two BIG
radiators (with radiative surface more than 200 cm^2) to each side of HDDs
using thermal paste. Please note: using those 'side fans' covers' doesn't
deliver from overheating!

-Mounting. Leave as much as possible space between lower and upper HDD!
Locate system speaker - if it is too close to HDD, dismount it and move
away!




Note on overclocking:

As always with overclocking, you do it on YOUR OWN RISC!

With both platforms (i875 and VIAKT880Pro) it is possible to overclock
processors to about 10% without any after-effects (means, hardware damage
or errors in PC GAMESS results).
Actually, everything is working fine even at 20% overclocking. But you must
have some margins of safety, when playing with such things. Remember, your
computers must be stable enough to work for months without errors. And
overclocking is a straight way to violence that stability.

To minimize loose of reliability you should follow several items:

-Do not exceed ANY voltages in your system. Exceeding voltages will degrade
your hardware. For some, maybe quite long period of time everything will
work fine and then glitches will break out.
-High-quality cooling system is necessary. Temperature of processor should
not exceed 45C (for Intel) and 50C (for AMD64), special memory cooling
plates must be used, side, input and output coolers must be installed into
system's case.
-Overclocker's special memory modules (for example, Corsair) with low
timings are needed.
-Power supply must be of extra quality and power (400 Watt is a minimum).

Note on AMD64 platforms and VIA KT880Pro chipset:

Unlike Intel, increasing system bus frequency will increase SATA link
operating frequency as well. Being normal at 150 GHz, SATA will become
inoperable at 170-175 GHz, and you won't boot until you change this back.
Moreover, OS damage is possible. We do not recommend you to violence this
limit. At the top of operational range (175GHz) SATA will work with errors
- so PC GAMESS and RAID will periodically crash. To avoid this, avoid
overclocking AMD64 on VIA chipset (you may use NVIDIA chipset instead), or
DO NOT approach too close the deadline.

Again, for both platforms, 10% overclocking is a practical limit.


4. OS and PC GAMESS tuning procedure - achieving best performance.

OS choice.

Among NT-family Microsoft OSs (NT5, Windows2000, Window2001 Server Edition,
Windows XP HE, Windows XP Professional Edition, Windows 2003 Server
Edition) you may choose one you prefer. Testing PC GAMESS with conventional
methods showed very slightly different results in calculations speed. The
only point you should notice is amount of free memory as it varies from OS
to OS considerably. Also do not hesitate over installing latest updates and
patches available for OS of your choice (with the only exception of SP2 for
Windows XP). Do not forget to make snap-shots of your OS with special
software or using build-in OS tools before any updates/patches applied, to
have an opportunity of roll-back.

*Note on SP2 for Windows XP.
Although PC GAMESS was tested under Windows XP with SP2 installed and no
problems or performance degradation were noticed, this Service Pack may
cause a number of compatibility issues between other programs installed on
computer where PC GAMESS runs, which in turn may lead to certain
instability.

Setting up OS and software environment.

There are some general rules one can hold to:

- OS's stability is inversely proportional to the number of programs
installed.
- Do not use any of 'optimizing-n-tuning software': you may win a bit in
performance, but you'll loose a lot in stability.
- Disable all OS or third-party monitors, virus scanners and other
resident software.
- Make sure that drivers for each device in your system is certified by
Microsoft Hardware Quality Labs; if certified drivers are not
available, use the most stable among the newest ones; you'll have to
perform your own tests on stability.

HDD storage system setting-up.

Since you use RAID, you have to configure RAID at first. This is normally
done thru special utility built-in a chip, which can be accepted thru a
System BIOS or its own BIOS during boot procedure. Please read instructions
on setting up your RAID in manual coming with your motherboard or add-on
card.

In a few words, you'll have to connect 2 equal SATA disks to 2 SATA port on
the motherboard/add-on card, then enable RAID operation of controller in
System BIOS, and reboot. While boot procedure, RAID BIOS will prompt to
change RAID configuration. If you agree, a controller specific utility will
be run. Using this utility, you may:

- Create RAID volume
- Delete RAID volume
- Configure RAID as RAID0 or as RAID1.

*Note on RAID.
After creation of RAID volume, OS (i.e. Windows) will see one RAID disk
instead of two. Operation with these two disks as they were one is
maintained by RAID driver. Please note that if you plan to use RAID volume
in a role of boot or system disk, you'll need floppy disk with that driver
at initial stage of Windows installation procedure. Otherwise, if RAID is
used as a working/storage disk only, you may install that driver later.

*Note on RAID level.

RAID0 and RAID1 are the basic RAID levels. Basically, RAID level 0 (aka
RAID0) is used to combine disks into one to achieve better performance, and
RAID1 is used to achieve better reliability by mirroring one disk to
another. Typically RAID1 doesn't give any benefit in sequential reading
(though there are exceptions on the market), and never benefits in
sequential writing. For this reason, we will not consider RAID1
configuration, and will focus on RAID0.

In simple, RAID0 uses two disks sequentially, striping them into logical
blocks (so called stripes), somewhat like clusters, while RAID controller
pretends to be an integral disk for a system. As a result, when data block
is requested by OS, RAID controller divides it between two member disks,
and each of them may retrieve its own portion of information simultaneously
with the other; these two disks work in parallel and thus resulting
throughput of RAID0 may be as high as doubled throughput of a member disk.
However, this is the ideal scenario. With this approach, seeking times
increase compared to single disk. Also, what happens if data block
requested by OS is smaller, than the stripe size? Obviously, performance
will degrade, and in classical RAID0 configurations (as default in every
controllers stripe size =128K) we may come to a paradox, when PC GAMESS
running with a single disk actually faster than one running on RAID0!

To avoid this, when formatting your RAID0 volume under OS, chose cluster
size twice as large as stripe size you've chosen when building RAID. Best
results in performance (almost doubling the throughput of a single disk)
were achieved when used 16K for a stripe size and 32K for a cluster size in
OS. Because of OS retrieves information from HDD storage system in units of
clusters, and cluster is twice as large as the stripe is, EVERY request
will be processed in parallel by two member disks. With this technique
sequential reading rates of 125 MB per second are possible.

Note on File System.

You may use any FS you like, but in real there are two of them to make
choice from: FAT32 and NTFS. FAT32 benefits from its simplicity and is
several percents faster than NTFS is, speaking of PC GAMESS operation. We
would recommend FAT32 for usage together with PC GAMESS, until your job is
large enough to overcome 4GB FAT32 limit in file size. For example, PUNCH
file may easily overcome this limit. In this case you'll have to use NTFS.


Note on FS configuring.

You may set several System Registry keys to achieve even better
performance, but be aware of changing other keys or using values other than
specified here:

To do this, open 'Start Menu', then click 'Run', type 'Regedit' into a box
and press 'OK'. Registry editing tool will now open. Then, in the menu
'Edit' choose 'Find' and type 'ReadAheadThreshold' into a text box. In a
minute, necessary registry section should be open. Please compare to this:

[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\FileSystem]
"NtfsDisable8dot3NameCreation"=dword:00000000
"Win31FileSystem"=dword:00000000
"Win95TruncatedExtensions"=dword:00000001
"NTFSDisableLastAccessUpdate"=dword:00000000
"ReadAheadThreshold"=hex:00,00,02,00

If what you see looks too different, use 'Find Next' command to search
through registry.

Then, you should be able to change keys' values. Please right-click on a
key you want to change in the right section of the Registry editing tool.
Context menu will appear, where 1st item will be 'Change'. Please choose
this item.
On next window opened, change value in a text box to your desired value,
then press 'OK' and edit next value.

As a result, this registry section should look like this:

[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\FileSystem]
"NtfsDisable8dot3NameCreation"=dword:00000001
"Win31FileSystem"=dword:00000000
"Win95TruncatedExtensions"=dword:00000000
"NTFSDisableLastAccessUpdate"=dword:00000000
"ReadAheadThreshold"=hex:00,00,04,00

Alternate way of modifying these registry keys it to create new text file
(using Notepad application) and copy previous section as is into this file;
save then that file with any name, then find it in Explorer and change file
extension from *.txt to *.reg. Then just double-click on that file will
initiate merging of your system registry and updated registry section. Just
answer 'yes' and your system registry will be updated.

*Note: on some web-sites you may find other keys from this section, which
supposedly can affect performance (like ContigFileAlloSize key and others),
but in real will degrade it. Be aware of tweaking FS and OS, as it is VERY
easy to make OS unreliable.

Finally: after configuring your OS and software environment, and careful
testing PC GAMESS running under tuned OS, make a snapshot of OS using OS
utility (make a recovery point) or third-party utilities. If something goes
wrong, you will be able to restore you tuned configuration in several
minutes.

PC GAMESS location.

Best scenario possible is to locate PC GAMESS on separate RAID0
volume, where nothing, but PC GAMESS will be resident. If you want to make
use of the rest of the RAID volume (suppose, your volume is as large as
400GB and you do not need all of them for PC GAMESS), create another
logical partition within the RAID volume: in this way, your files will
never be mixed with PC GAMESS work files, and no fragmentation will occur.
If you do not plan using your computer for anything, but PC GAMESS, you may
also create System disk within a RAID volume. In this case, however, you
should make PC GAMESS partition first, then System partition and only then
Storage partition. Otherwise, performance will degrade. All these
manipulations are possible with special disk managing tools, like Partition
Magic 8.0 or others.

*Note on swapping file:

While it is best solution to locate swapping file on a high-speed
separate disk, if it is not needed for some reason you must locate it on PC
GAMESS working disk to achieve best possible performance. This situation is
normal when assembling node for a cluster, for example.


PC GAMESS specific settings.

Several useful keys for PC GAMESS itself will enhance performance
considerably.
SYSTEM card:
- VOLSIZ=512. This key will force splitting all working files into
pieces of 512 MB in size. If amount of memory on your computer greater
than 512 MB, OS overhead will be considerably reduced and efficiency
will dramatically rise.
- AIOBUF=8192 This key will set buffer size for reading/writing
integrals to 8Mb. This value should be found out experimentally.
Increases to some extent reading/writing performance of HDD storage
system when OS cache is disabled (see below)
- IOFLGS (8) =16384 - forbids using OS caching. Use this keys with care
as it may cause performance degrade as well as performance boost.
Ideal for using on nodes, where nothing but PC GAMESS runs. On
workstations, any competitive process may cause loose of synchronism
between IO subsystem and CPU and thus will considerably reduce HDD
storage system throughput.

SMP card:
- HTTFIX=.T. - enables Hyper Threading support for Intel processors.
This key must be present if HTT is enabled in hardware.

P2P card:
- P2P=.T. DLB=.t. MIXED=.T. Presence of this group enables Peer-to-Peer
interface for network communication when nodes are joined into a
cluster. With these keys using of different platforms (for example,
Intel and AMD64) becomes possible. Also, due to dynamical balancing of
nodes load, more of the task distributed to more powerful node, which
avoids idling of faster nodes waiting for slower to finish their job.
It becomes evident when in cluster there are AMD64 and Intel P4 nodes
are mixed: AMD64 looses in speed at 2e integrals and 2e gradient
evaluation, but overperforms Intel P4 during SCF calculation. To
smooth this difference it is useful to engage dynamical loading
technique.

And, finally, some minor advices:

- Assign lowest level of priority possible to PC GAMESS. OS will
operate then in the most effective way.
- Periodically check you PC GAMESS disk (RAID) for errors. Before any
large job check everything out to be in normal, de-fragment PC GAMESS
disk.
- If you get FSF fatal error you should consider reduce your
overclocking rate or, if no overclocking is in effect, carefully test
your hardware parts. You may check if there is okay with CRC
controlling key in PC GAMESS. This will slow everything down (5-9%)
but will give you assurance that your HDD storage system operates
normally.


Summary: very simple. Carefully chosen hardware parts, understanding
bottlenecks in conventional PC GAMESS calculations and workarounds for
them, fine tuning of OS and software environment, not violating
overclocking margins gives one possibility to assemble very reliable, fast
and not expensive workstation/node for quantum chemistry works. Isn't that
what you wanted?