time based: is the time to: HD:head positioning , SSD: time to send command to ROM chip HD:read/write time (disk speed - rpm), SSD: time to write/read (time to ssd rom chip receive bytes) that's time based what is fast por read? consider that time based must know that disk is doing a I/O and that you have a time to end, this time to end is another time in algorithm for example: NBD (network block device) time to send read message + time to send command to rom or head positioning read/write time: time to nbd server return the read/write bytes what algorithm should do? calculate all time or all mirrors, including time to end current request (if only one request could be processed, or if allow more than 1 request, the time spent to start our command) after all time calculated, select the minimal value/device that's time based it's not based on round robin it's not based on closest head it's based on device speed to: *(1)position head/send rom command *(2)read/write time (per total of bytes read/write) *(3)time to start out request command (if don't allow more than 1 request per time, don't have a device queue) the total time per device will tell us the best device to read if we mix, nbd + ssd + hdd (5000rpm) + hdd(7500rpm) + hdd(10000rpm) + hdd(15000rpm) we can get the best read time using this algorithm the problem? we must run a constante benchmark to get this values *(1) *(2) *(3) and calculate good values of time spent on each process resuming... whe need a model of each device (simple-constants or very complex-neural network?), and calculate time spent per device nice? 2011/2/2 Robin Hill <robin@xxxxxxxxxxxxxxx>: > On Tue Feb 01, 2011 at 09:12:11PM -0200, Roberto Spadim wrote: > >> but the best algorithm is time based (minimize time to access data) >> > And what do you think takes the time accessing the data? In a rotating > disk, it's moving the heads - that's why the current strategy is nearest > head. In an SSD there's no head movement, so access time should be the > same for accessing any data, making it pretty much irrelevant which > strategy is used. > > Cheers, > Robin > -- Roberto Spadim Spadim Technology / SPAEmpresarial -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
