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

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.