iostat stops reporting IO after 2TB

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xerces8
Posts: 28
Joined: 28 Aug 2012, 11:17

iostat stops reporting IO after 2TB

Postby xerces8 » 03 Aug 2016, 21:11

I am running a long dd copy on a large 5TB disk (sda).
After I while I noticed that "iostat 2" prints 0 kb/s for sda, even if transfers are in progress.

The tps value is updated, but read/write speed and amount read/written is all 0.

I'm using v4.8.0 64 bit (kernel 4.1.27).

xerces8
Posts: 28
Joined: 28 Aug 2012, 11:17

Re: iostat stops reporting IO after 2TB

Postby xerces8 » 02 Apr 2017, 16:26

It is the same in v4.9.3.

I guess it is a limitation of the 32 bit API used by the 32 bit userspace apps.

Details:
- count stops at 2TB with 64 bit kernel
- with 32 bit kernel, it wraps around to zero each 2TB (I guess it is 2TB as I was not around to see the exact moment of wraparound, I just saw that after 5TB it was showing less than 2TB)


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