Russell Jones wrote:
Emmanuel Briot wrote:
Hi,
I was wondering whether there is any tool in linux that can be used to
simulate a slow file system ?
I would need this to test the application I am working on, since some
customers are not using fast machines (some are even using Windows with
encrypted file systems). I would add such a tool to the very nice set
of tools on linux like valgrind, sysprof and memprof...
While we are at it, any way to simulate a slow network ?
Thanks in advance
Emmanuel
Slow network: I'd think you can tell most network cards to run in
100Base-T or 10Base-T.
ifconfig eth0 media 10baseT ?
Slow disk: run using Xen or KVM? I'm not sure how much control you have
over the resources allocated, but I'd think slowing the processor would
go some way to simulating a system with a slow hard disk as it would
impact data transfer rates.
the chief bottleneck of disk access is the disk drive
itself. Disk-head motion introduces delays on the order
of milliseconds. In fact, compared to the speed of
modern CPUs, even the memory on the motherboard is
slow...this is why CPUs have L1 and L2 (and some
even have L3) cache.
Giving a xen partition a small slice of CPU will
have negligible impact on disk access. On a
3 GHz CPU, a Xen partition allowed only 1% of
CPU is effectively the same as a 30 MHz CPU,
which is STILL capable of buffering write()s
and unbuffering read()s faster than any mechanical
disk drive doing I/O on a filesystem is capable
of, because while the disk head is seeking, the
CPU is *STILL* running marshalling and unmarshalling
the I/O data, and then the disk drive controller
comes in, and does DMA (direct memory access,
which means CPU speed doesn't even play a
part.)
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