[Lustre-devel] read ahead
Peter Braam
Peter.Braam at Sun.COM
Thu Dec 13 11:09:28 PST 2007
Tom.Wang wrote:
> Hi, Peter
>
> I just talked with Matt about his pCIFS test. In his test, there are 2
> clients, 2 OST, (stripe_count =2, stripe_size=1M).
> Each client run 1 thread to read a shared file. Each thread(client)
> will only read data of the shared file from 1 OST, so
> read request is discontiguous (1M step stride I/O) for each of thread,
> which will not trigger read-ahead, because
> read-ahead window will be reset once it met discontinuous read
> request. So kept read-ahead in the same step
> of stride step ((stripe_count -1) * stripe_size) instead of
> contiguous could just fix this problem, and it is what we are
> working now.
>
Finally! This makes a lot of sense.
> Btw: we also need this in lustre collective read ADIO driver,
> since we will also need reorganize the data as 1client-> 1OST
> model like pCIFS does.
I now see why this stripe behavior with read-ahead is so very important
for Lustre in some cases.
It would also be important to know that in basic cases we really get as
good read performance as write.
- Peter -
> Another alternative way maybe move read-ahead mechanism to
> osc layer, but maybe a bad idea.
> Thanks
> WangDi
>
More information about the lustre-devel
mailing list