Hi Ed,
Thanks for the response. Below are the details which explains the
scenario better.
The system can be considered as one with dual CPU complex, but a single
SSD. There are 2 operating systems, OS-1 and OS-2 running on each of the
CPU complex, OS-1 boots first and takes control of the SSD and starts the
target. OS-2 which boots up later uses initiator to connect to target over
an interface connecting the 2 CPU complex. There is no switch in between,
its a back to back Ethernet network over which AoE is being used by OS-2
for all disk accesses.
Now, at some point in time, OS-1 has to be shut down, which means target is
not available anymore. OS-2 will now start the target on loopback interface
using "vbladed 0 0 lo /dev/sda". As this system is going to run for a long
time, i want to understand the overhead that is there in disk access from
the POV of applications running on OS-2. I want to compare the AoE based
access mechanism in the above scenario with the case where OS-2
applications are directly accessing the SSD.
Now, all the queries below are for this case where OS-2 has the initiator
which tries to connect to the target which is also running in OS-2, no
network in between. Not sure if your previous responses would still be
valid for this specific case as for example MTU might not be a
consideration from the actual data transfer POV.
a. Wanted to understand if the AoE model has specific optimizations
done to make this as close as possible to a regular local disk access.
b. I see the Linux storage stack @ https://upload.wikimedia.
org/wikipedia/commons/3/30/IO_stack_of_the_Linux_kernel.svg <http://%2522/>,
I was wondering about the overhead involved in accessing storage from
application POV once I restart the AoE target locally.
i. Overhead
from the perspective of additional LOC involved as compared to a local disk
access
ii. Overhead
from the perspective of throughput possible as compared to a local disk
access
c. Do you think further optimizations are theoretically possible to
take care of this specific scenario to make it just like a regular local
disk access?
Thankyou,
nivin
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