32 bit architectures and storage speeds

Jan Safranek jsafrane at redhat.com
Fri May 3 08:54:52 UTC 2013


Hi,

I'm implementing Block Server Performance Subprofile and one of the
values it reports is nr. of sectors read/written from/to a block device.

On 32-bit architectures, these values are provided by kernel with 32-bit
precision. If someone is using iSCSI over 10Gb/s link, the 32 bit
counter overflows in roughly 1600 seconds. Therefore my provider should
periodically detect this overflow and recalculate 64 bit number out of
it. It's not so difficult, but:

- Do we need to support 32 bit architectures at all?
- What is the maximum read speed we need to support? I need to set the
timers right, so I don't miss an overflow of the counters, and still not
take too much CPU. Is it 10Gb/s? What will be iSCSI/FC/SSD speed in 10
years? Remember, the 32-bit machine might be virtual, running on really
powerful HW.

Jan


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