I'm testing an active/active setup that uses md for raid0 and was
hoping for some feedback.
The basic design has a storage device that runs vladed (aoe-storage)
and an aoe initiator (controller) that creates a raid0 using mdadm
from the aoe devices. From there, lvm (clustered/clvm) slices out
storage for sharing block devices. I don't want to concentrate on the
layers above that (clustered file systems, etc) but mainly the active/
active portion of this interacting with raid0 (via md not lvm) and aoe.
Some diagrams that may help in understanding...
-----
"Physical" diagram:
(export network block devices [ iscsi, aoe, etc] )
-----------
/ \
active / \ active
+-------------+ +-------------+
| controller1 | | controller2 |
+-------------+ +-------------+
\ /
+---------+
|
+-------------+ +-------------+
| aoe-storage | --- drbd raid1 --- | secondary |
+-------------+ +-------------+
-----
Layer diagram:
+-----------------+
| (net block dev) | controller1/2
+-----------------+
| lvm2 clustered | controller1/2
+-----------------+
| md: linux-raid0 | controller1/2
+-----------------+
| aoe initiator | controller1/2
+-----------------+
| aoe target | aoe-storage
+-----------------+
My main concern is interaction with buffer cache and the consistencies
of the md devices between the controllers (probably not page cache
since these are block devices?). Will direct/O_DIRECT bypass this
keeping the state of the data purely on the aoe-storage device? I
have a test setup of this running with no issues so far connecting to
the controllers that run iscsi-target (iet) in blockio mode, thus
bypaassing buffer/page cache.
Any feedback is appreciated.
--
Matth
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