Thanks very much.
I will try DRBD later
But I want to figure this out.

I have export disk using tgtd and load disk on another server using
iscsiadm with infiniband  of iser protocol.
Does ISCSI/Iser have any cache on it.


2015-03-22 15:28 GMT+08:00 Adam Goryachev [off-list ref]:

On 22/03/2015 16:00, lingli tang wrote:

quoted

Thanks for reply.

I have create a raid1 with two fusion io PCIe flash disk:
mdadm --create /dev/md/master --name=master --level=1 --raid-devices=2
/dev/fioa2 /dev/mapper/mpathc
/dev/fioa2 is local disk on server A and /dev/mapper/mpathc is a iscsi
load disk export from server B.

After that we mkfs.ext4 on /dev/md/master and mount with 'sync' option on
/data1
and we will run mysql binlog on it.
In order to avoid data loss  of mysql binlog we have set
sync_binlog=1. so every sql commit will call fsync() to flush to disk.

according to your description. if we reboot the server A, the two disk
data on different server will be the same.
but after the server A restarted, we assemble the two disk on two
server, data is different on the two server, disk on server B lost
more than one sql commit.

I have checked it with strace 'mysqld' on Server A.
I found a sql commit and fsync() on binlog file handle on server A but
this sql can not find in assembled disk on server B.

I also test it with two SAS disk, Server B still has more than one sql
commit lost.

Sounds like you might be better using something like DRBD (www.drbd.org)
which has different modes, one of which will do what you are asking (not
respond until both systems have confirmed the data is written to the local
disk).

In your current case, even if md is correctly writing to both underlying
'devices' you have multiple layers under one of the devices, so you should
confirm that *all* of those layers are properly passing through the data
without any caching/etc.

Regards,
Adam