Test OpenSuSE(AHCI) FreeBSD(AHCI)
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SSD(vfat 25GB) 41+/-2 MB/s at 4-10% 15+/-0 MB/s at 2% CPU
SSD(raw 25GB) 26+/-1 MB/s at 4-10% CPU 48+/-0 MB/s at 1% CPU
SSD(ext3 25GB) 39+/-5 MB/s at 10-15% CPU 34+/-0 MB/s at 14% CPU
SSD(ext2 25GB) 42+/-1 MB/s at 10-15% CPU 32+/-0 MB/s at 10% CPU
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Test OpenSuSE (AHCI off) FreeBSD (AHCI off)
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SSD(vfat 25GB) 22+/-4 MB/s at 6-19% CPU --
SSD(raw 25GB) 33+/-4 MB/s at 7-14% CPU 41+/-0 MB/s at 1% CPU
SSD(ext2 25GB) 27+/-6 MB/s at 6-14% CPU --
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Question 1:
Can anybody explain to me, why writing to a SATA-I device with AHCI consumes so much CPU time using Linux, while it takes almost no CPU time on FreeBSD 6.2 ? Especially comparing values of writing to the raw device?
Question 2:
Can anybody explain to me, why writing to a solid state disk (a kind of memory that always has the same constant bandwidth) has such big standard errors in writing rate using Linux (between 1 to 6 MB/s error) while FreeBSD gives an almost constant writing rate (as one would expect it for a SSD) ?
Question 3:
Why is writing to a raw device in Linux slower than using e.g. ext2 ? And why is Linux writing rate much lower (-12.5 % for the best case) compared to writing rate of FreeBSD?
Question 4:
When writing to the SATA-II HDD Linux is around 10% slower than FreeBSD when using ext3, but around as fast as FreeBSD when writing raw. Why?
How can I improve the speed of Linux,