Problem as follows: 1) Plug in an external USB drive. 2) Mount it anywhere. Doesn't matter how. 3) Copy a few GB of data to the drive from a non-USB disk. 4) Watch the load average "climb" to 5.x, sometimes 10.x or more. Why? This on an otherwise unloaded system. Doesn't matter how many cores, how much RAM, 32/64 bit, etc. Why should copying some files to a USB drive cause load averages to climb so high? (and network monitors to freak out?)
On Apr 20, 2012 2:42 AM, "Lists" <lists at benjamindsmith.com> wrote:> > Problem as follows: > > 1) Plug in an external USB drive. > > 2) Mount it anywhere. Doesn't matter how. > > 3) Copy a few GB of data to the drive from a non-USB disk. > > 4) Watch the load average "climb" to 5.x, sometimes 10.x or more. Why? > This on an otherwise unloaded system. Doesn't matter how many cores, how > much RAM, 32/64 bit, etc. > > Why should copying some files to a USB drive cause load averages to > climb so high? (and network monitors to freak out?)It's just a number. Is the system any slower? Linux adds I/O wait time to the load average calculation. -- Giovanni
On Fri, Apr 20, 2012 at 12:42 AM, Lists <lists at benjamindsmith.com> wrote:> Problem as follows: > > 1) Plug in an external USB drive. > > 2) Mount it anywhere. Doesn't matter how. > > 3) Copy a few GB of data to the drive from a non-USB disk. > > 4) Watch the load average "climb" to 5.x, sometimes 10.x or more. Why? > This on an otherwise unloaded system. Doesn't matter how many cores, how > much RAM, 32/64 bit, etc. > > Why should copying some files to a USB drive cause load averages to > climb so high? (and network monitors to freak out?)The CPU has to do the work of the transfer over usb - which is why it is cheap. Real disk controllers use DMA without a lot of CPU involvement. -- Les Mikesell lesmikesell at gmail.com
On Friday, April 20, 2012 10:54:51 AM Les Mikesell wrote:> The CPU has to do the work of the transfer over usb - which is why it > is cheap. Real disk controllers use DMA without a lot of CPU > involvement.And this includes USB 3.0, incidentally. I have found that on my Fedora 14 (soon to be C6) laptop with a USB 3.0 ExpressCard interface that the load is less on USB 3 and it is on the laptops built-in USB 2 ports. YMMV.