32 bit architectures and storage speeds

Jan Safranek jsafrane at redhat.com
Fri May 3 08:59:30 UTC 2013


On 05/03/2013 10:54 AM, Jan Safranek wrote:
> 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.

Also, second thought: watching for overflow means that the provider must
be always on, it cannot be unloaded if it is idle.
(that can be of course admin-configurable).

Jan



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