raid1 read io balancing algorithm

raid1 read io balancing algorithm

[struhlo]

 
hello,
 
how can i check set what read io scheduling/balancing is done in radi1 over md raid1 devices ?
 
I have host based mirror over san devices, and to be honest i haven't found any mention in the docu nor raid.wiki.kernel.org about how the raid1 read balancing is done.
 
thanks
br/s
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Re: raid1 read io balancing algorithm

[Roberto Spadim]

hi, from what i remember, it's done only with device "last position"
AKA "disk head position"
the device with head position near to position being read is "selected"
on sequencial reads, the last used device is used, considering that
for sequencial reads a single disk is faster, because we don't waste
3ms to positioning head to sector, that's near true if you don't have
diferent devices speed (7200rpm + 10000rpm + 15000rpm + ssd)

the best source of this information is source code of raid1.c
it's a function (i don't remember the name, but something like read_balancing)

Re: raid1 read io balancing algorithm

[Roberto Spadim]

hi, from what i remember, it's done only with device "last position"
AKA "disk head position"
the device with head position near to position being read is "selected"
on sequencial reads, the last used device is used, considering that
for sequencial reads a single disk is faster, because we don't waste
3ms to positioning head to sector, that's near true if you don't have
diferent devices speed (7200rpm + 10000rpm + 15000rpm + ssd)

the best source of this information is source code of raid1.c
it's a function (i don't remember the name, but something like read_balancing)

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