Re: [libvirt] NFS over RDMA small block DIRECT_IO bug

On Sep 5, 2012, at 4:02 PM, Avi Kivity wrote: > On 09/04/2012 03:04 PM, Myklebust, Trond wrote: >> On Tue, 2012-09-04 at 11:31 +0200, Andrew Holway wrote: >>> Hello. >>> >>> # Avi Kivity avi(a)redhat recommended I copy kvm in on this. It would also seem relevent to libvirt. # >>> >>> I have a Centos 6.2 server and Centos 6.2 client. >>> >>> [root@store ~]# cat /etc/exports >>> /dev/shm 10.149.0.0/16(rw,fsid=1,no_root_squash,insecure) (I have tried with non tempfs targets also) >>> >>> >>> [root@node001 ~]# cat /etc/fstab >>> store.ibnet:/dev/shm /mnt nfs rdma,port=2050,defaults 0 0 >>> >>> >>> I wrote a little for loop one liner that dd'd the centos net install image to a file called 'hello' then checksummed that file. Each iteration uses a different block size. >>> >>> Non DIRECT_IO seems to work fine. DIRECT_IO with 512byte, 1K and 2K block sizes get corrupted. >> >> >> That is expected behaviour. DIRECT_IO over RDMA needs to be page aligned >> so that it can use the more efficient RDMA READ and RDMA WRITE memory >> semantics (instead of the SEND/RECEIVE channel semantics). > > Shouldn't subpage requests fail then? O_DIRECT block requests fail for > subsector writes, instead of corrupting your data. But silent data corruption is so much fun!!