WHAT’S THE FASTEST RAID STRIPE SIZE?
The test: When configuring a RAID array, you have the
option of choosing from several different stripe sizes. These
data “stripes” are the chunks of data that files are broken into
before being written to each drive in the array. Stripe size
options usually range from 16K up to 128K, but which stripe
size is best?
To find out the impact of stripe size on performance, we
grabbed two Maxtor 250GB Ultra series drives and attached
them to a Promise ATA RAID con-
troller. We configured a striped
array for each of the controller’s
stripe-size options, ran HD Tach on
each array, and isolated the read
speed results. We also transferred
three differently sized batches of
files from our test system’s hard
drive to each RAID array and
recorded the transfer times.
The results: Testing showed there isn’t a huge difference in
performance among stripe sizes, at least in the 16K-to-128K
range our controller allows (some controllers offer stripes as
large as 512K). But the little performance advantage we did
observe scaled with the smaller stripe, so if your array is set
to a “default” stripe size you might want to make sure it’s the
minimum.STRIPE SIZE COMPARISONS 16K STRIPE 32K STRIPE 64K STRIPE 128K STRIPE
HD TACH^
Average read speed (MB/sec) 97 97 95 95
*Small file write (sec) 32 30 31 33
**Medium file write (sec) 71 75 74 76
***Large file write (sec) 21 23 21 22
Best scores are bolded.
*Test involved transferring 94.5MB of files averaging 20K-35K.
**Test involved transferring 2.27GB of files 4MB-6MB.
*** Test involved transferring one 749MB file.Which is Faster: a
Two-, Three-, or Four-
Drive RAID Array?
The test: While most RAID
arrays consist of two drives, we
wondered how much additional
performance could be achieved
by moving to a three- or four-
drive array. To test this theory, we
gathered four Maxtor 250GB Ultra
series parallel ATA drives and
tested a single drive first, then
RAID arrays consisting of two,
three, and four drives. The drives
were connected to a Promise Fast
Trax TX4000 ATA PCI RAID con-
troller using an Intel 865GBF chip-
set on an Intel motherboard. Todetermine each array’s overall
performance we ran HD Tach
three times on each drive config-
uration and recorded the results.The results: The results were
interesting for several reasons.
While the two-drive array deliv-
ered stunning performance,
adding a third drive practically
maxed out the 32-bit PCI bus.
The three-drive array achieved
a maximum burst speed of
127MB/sec, which is damn close
to the 133MB/sec limit of the PCI
bus, which means the drives are
simply saturating the bus with
data. It also could mean that the
three-drive array is capable of
transferring data even faster if
given more headroom.
Even more interesting than
the results of adding a thirddrive is the discovery that add-
ing a fourth drive results in a
performance drop. Because the
PCI bus was already saturated
with just three drives, adding a
fourth simply added more over-
head to the whole operation,
resulting in slower performance
overall. Ain’t that a bitch?
You might be wondering
to yourself how the Serial
ATA interface, with its extra
17MB/sec of bandwidth would
compare with parallel ATA
(150MB/sec versus 133MB/sec).
Common sense suggests the
increased bandwidth would
improve the performance of a
four-drive array. However, as
long as a controller card, SATA
or otherwise, is plugged into the
133MB/sec PCI bus, the band-
width limitation persists.RAID PERFORMANCE SINGLE DRIVE TWO DRIVES THREE DRIVES FOUR DRIVES
HD TACHAverage read speed (MB/sec) 47 95 113 107
Best scores are bolded.JUNE 2004 MAXIMUM PC 37