Performance issues in 64-bit platforms
Hi everybody,
although the following question is not debian-specific ( at least I hope so ), I'm posting it here, betting on the 64-bit architecture knowledge of the list.
I have two 64-bit systems, both running Debian testing. One is a Core2 Duo
laptop@2GHz, running a 32-bit Debian, the other is an AMD dual core 3800+ desktop computer, running 64-bit Debian.
I'm benchmarking both systems and I've run "hdparm -tT" on both. Now, the laptop has a typical laptop disk, namely a TOSHIBA MK1234GSX. The desktop on the other hand, has two Western Digital Raptors, 80G each, in software RAID0, and a slower/bigger typical desktop disk, namely a Seagate ST3160812AS, that is sitting outside the RAID configuration.
The outputs of "hdparm -tT" are as follows:
-----------------------------------------------------------------------------------------------------------
1 - LAPTOP:
/dev/sda:
Timing cached reads: 5788 MB in
1.99 seconds = 2901.82 MB/sec
Timing buffered disk reads: 102 MB in 3.02 seconds = 33.78 MB/sec
2 - DESKTOP WD raptors in RAID0 (root partition):
/dev/md2:
Timing cached reads: 1920 MB in 2.00 seconds =
960.95 MB/sec
Timing buffered disk reads: 410 MB in 3.01 seconds = 136.14 MB/sec
3 - DESKTOP single WD raptor:
/dev/sdb:
Timing cached reads: 1938 MB in 2.00 seconds = 969.44 MB/sec
Timing buffered disk reads: 206 MB in
3.02 seconds = 68.24 MB/sec
4 - DESKTOP single Seagate:
/dev/sda:
Timing cached reads: 1926 MB in 2.00 seconds = 963.75 MB/sec
Timing buffered disk reads: 208 MB in 3.01 seconds = 69.02 MB/sec
-----------------------------------------------------------------------------------------------------------
Now, off to the questions:
1) Why are cached reads on the Laptop so much faster (case 1 vs. 2,3 and 4)??? The laptop has 1G of memory (probably a cheap one as well, to keep the cost low), the desktop has 2G of memory, fastest one my money could buy...
2) Shouldn't the "notorious" WD raptor greatly outperform the Seagate when comparing single disk performance (case 3 vs. 4)? After all, the WD costs 2 times the price of the Seagate (or was it even more..?).
There seems to be some kind of limiting factor/bottleneck on my desktop that is restricting performance. I don't believe there's such a big difference (in terms of performance) between the Intel Core Duo and the AMD dual core architectures, capable of yielding such results (3x faster in cached reads), especially when we're talking about a "power-sensitive" laptop versus a mighty data-crunching desktop machine.
btw. I found out that I cannot set any HD parameters from within hdparm, for both systems. It always fails with the message:
Inappropriate ioctl for device
so the Serial ATA drivers don't have the relevant ioctl() calls implemented? or maybe i'm missing something here...
Thank you all for your time, and if you feel this is out of topic, plz. let me know and I will post somewhere else.
Dimitris
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