On Sun, May 17, 2009 at 02:16:01PM +0300, Ahmed Kamal wrote: > I am wondering whether the reliability of solaris/zfs is still guaranteed if > I will be running zfs not directly over real hardware, but over Xen > virtualization ? The plan is to assign physical raw access to the disks to > the xen guest. I remember zfs having problems with hardware that lies about > disk write ordering, wonder how that is handled over Xen, or if that issue > has been completely resolved
You can read the frontend sources here: http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/xen/io/xdf.c If both dom0 and domU are Solaris, then any disk cache flushes are passed through via FLUSH_DISKCACHE. If the dom0 is Linux, then we attempt to emulate a flush by using WRITE_BARRIER (annoyingly, this requires us to write a block as well, so in this case, we cache one). In the backend (xdb or xpvtap), we pass along the flush request, either via an in kernel flush: 683 (void) ldi_ioctl(vdp->xs_ldi_hdl, 684 DKIOCFLUSHWRITECACHE, NULL, FKIOCTL, kcred, NULL); or via VDFlush() in the VirtualBox code we use (which essentially ends up as an fsync()). Thus as long as the ioctl and/or fsync are obeyed, things should be good. Hope that's clearer. regards john _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
