I have a Quantum Fireball SE 4.3G drive that claims UDMA
capability. I am getting 7.8Mb/s out of this drive. This is
fast, and I can't complain, however it is nowhere near the rated
capacity of the drive which is 33Mb/s on the SE pdf datasheet.
Further inspection of the datasheet indicates that the drive has
an internal buffer size of 128k. When I do an "hdparm -i" on the
drive, it indicates:
1 root@red:/# hdparm -i /dev/hda
/dev/hda:
Model=QUANTUM FIREBALL SE4.3A, FwRev=API.0A00, SerialNo=33473491
Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
RawCHS=14848/9/63, TrkSize=32256, SectSize=512, ECCbytes=4
BuffType=3(DualPortCache), BuffSize=80kB, MaxMultSect=16, MultSect=16
DblWordIO=no, maxPIO=2(fast), DMA=yes, maxDMA=2(fast)
CurCHS=14848/9/63, CurSects=8418816, LBA=yes, LBAsects=8418816
tDMA={min:120,rec:120}, DMA modes: sword0 sword1 sword2 mword0 mword1 mword2
IORDY=on/off, tPIO={min:120,w/IORDY:120}, PIO modes: mode3 mode4
As you can see, it says "BuffSize=80kB". That is NOT 128k for
sure.
Some other interesting things... the pdf datasheet says that the
drive has an internal data transfer rate (disk to buffer) of
158Mb/s. Other parts of the sheet refer to MEGABYTE as MB, so
I'm assuming that Mb means megabit which makes more sense than
does Megabyte for the number "158". So at 158 megabits per
second data transfer from disk to buffer, we get:
158 / 8 = 19.75MB/s or 19 megabytes per second.
This is NOT the rated 33megs per second that the sheet claims for
UDMA operation. The rate for PIO/DMA is 16.6Mb/s. I get 7.8Mb/s
or roughly half of spec. Does this mean that if I use UDMA, I
can expect around double, or 15Mb/s? If so, that is far from
33Mb/s, and still not quite even the calculated 19.75Mb/s that
the internal buffer supports.
What gives with these specs? What is even more confusing is that
at the bottom of the document it says "Quantum defines a megabyte
as 1000000 bytes". That adds a hell of a lot of confusion to
their datasheets, and accepted standards. I realize that Quantum
is not the only drive manufacturer doing this however - they all
do it.
Question: How can one tell what the true speed will be for a
given drive from a given manufacturer? Is there a formula? My
formula is currently: rated-internal-buffer-rate/8 * 0.40
Is this accurate?
At any rate, my kernel related question on this topic is, aside
from the current support in the kernel, what new efforts are
underway to get the most out of a hard disk? Does one need to go
with a RAID array to get 33Mb/s?
Can anyone shed light on getting more speed out of these drives?
I'm currently using:
/dev/hda:
multcount = 16 (on)
I/O support = 1 (32-bit)
unmaskirq = 0 (off)
using_dma = 0 (off)
keepsettings = 0 (off)
nowerr = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 524/255/63, sectors = 8418816, start = 0
Now back to your regularly scheduled programming. (pun intended)
-- Mike A. Harris - Computer Consultant - Linux advocateEscape from the confines of Microsoft's operating systems and push your PC to it's limits with LINUX - a real OS. http://www.redhat.com
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