search for: directsync

On 7/29/19 3:51 AM, Ming-Hung Tsai wrote: > I'm curious that why librbd sets this limitation? The rule first > appeared in librbd.git commit d57485f73ab. Theoretically, a > write-through cache is also safe for VM migration, if the cache > implementation guarantees that cache invalidation and disk write are > synchronous operations. > > For example, I'm using Ceph RBD

I'm curious that why librbd sets this limitation? The rule first appeared in librbd.git commit d57485f73ab. Theoretically, a write-through cache is also safe for VM migration, if the cache implementation guarantees that cache invalidation and disk write are synchronous operations. For example, I'm using Ceph RBD images as VM storage backend. The Ceph librbd supports synchronous

...harserial0 -device isa-serial,chardev=charserial0,id=serial0 -device usb-tablet,id=input0 -vnc 127.0.0.1:1 -vga cirrus -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 For fun I tried a few different cache options to try to force a bypass the host buffercache, including writethough and directsync, but the number of virtio kernel threads appeared to explode (especially for directsync) and the throughput dropped quite low: ~50% of "none" for writethrough and ~5% for directsync. With cache=none, when I generate write loads inside the VMs, I do see growth in the host's buffer...

...e. When a migration is considered to be unsafe it is rejected unless the --unsafe option is prodivided. As a part of those checks virsh considers the cache settings for the underlying storage resources. In this context only cache="none" is considered to be safe. I wonder why cache="directsync" might be harmfull as it bypasses the host page cache completely. Regards, Michael

Greetings Has libvirt dedicated page cache area for guest ? If not - what is the difference between cache='none' and cache='directsync' ? >The optional cache attribute controls the cache mechanism, possible >values are "default", "none", "writethrough", "writeback", "directsync" >(like "writethrough", but it bypasses the host page cache) and >"unsafe&...

...dge instead to go through to macvtap, so I'm not sure what is the best in this case. Regarding disk, since it's LVM I've chosen to go to cache mode none and IO mode native. Also here cannot judge what's the best setup for the workload. I'm undecided to use IO mode threads along directsync cache mode. Finally I've set "ionice -c 1 -p <qemu-pid> -n 0" and "renice -n -10 <qemu-pid>" for the interested VM that I want to get best performance possible. Even with the above setup, the MSSQL VM has performance similar to the old machine running ESXi 5.5,...

...s with LVM. After chasing down this issue some more and attempting various things (build the image on Fedora29, build a real XFS filesystem inside a VM and use the generated qcow2 as a basis instead of virt-format).. ..I've noticed that the SATA disk of each of those guests were using 'directsync' (instead of 'Hypervisor Default'). As soon as I switched to 'None', the XFS issues disappeared and I've now applied several consecutive kernel updates without issues. Also, 'directsync' or 'writethrough', while providing decent performance, both exhibited...

...cache=writeback without problems, to a CentOS7 host, live migration aborts with an error: [root@source] virsh migrate Totem --live --copy-storage-all --persistent --verbose --unsafe qemu+ssh://root@172.31.255.11/system error: unsupported configuration: native I/O needs either no disk cache or directsync cache mode, QEMU will fallback to aio=threads This error persists even if the VM config file is changed to use "io=threads". Of course, the running image continue to have "io=native" on its parameters list, but it does not really honor the "io=native" directive, so...

Hi, I tried two different approaches. 1.) Convert an existing Image with qemu-img ================================================ qemu-img convert -t directsync lubuntu-14.04.3-desktop-i386.iso sheepdog:lubuntu1404.iso ================================================= results in ==================================================== root@orion2:/var/lib/libvirt/xml# virsh vol-dumpxml --pool herd lubuntu1404.iso <volume type='network'> <n...

...h to macvtap, so I'm > not sure what is the best in this case. > > Regarding disk, since it's LVM I've chosen to go to cache mode none and IO mode native. Also > here cannot judge what's the best setup for the workload. I'm undecided to use IO mode threads > along directsync cache mode. > > Finally I've set "ionice -c 1 -p <qemu-pid> -n 0" and "renice -n -10 <qemu-pid>" for the interested > VM that I want to get best performance possible. > > Even with the above setup, the MSSQL VM has performance similar to the old ma...

...on about NFS datastore and unsafe migration. When migrating a virtual machine having a virtio disk in writeback cache between two hosts sharing a single NFS datastore, I get the following error: "Unsafe migration: Migration may lead to data corruption if disks use cache != none or cache != directsync" I understand why libvirt alerts for unsafe migration in cases where no coherency is enfoced by the underlying system; however, is it really the case for nfs? From what I know (and from the man page), by default nfs has open-to-close consistency, which seems quite right for migrating a...

...> I have an iSCSI disk with a backup. I want to use that backup on another > machine to test putting back data. > > What I use now is this: > ---- > <disk type='block' device='disk'> > <driver name='qemu' type='raw' cache='directsync' io='native'/> > <source dev='/dev/disk/by-id/scsi-36e843b6afdddf65dc4e9d4dc2dab66de'/> > <target dev='vdh' bus='virtio'/> > <address type='pci' domain='0x0000' bus='0x00' slot='0x0c' &g...

...e Totem --live --copy-storage-all --persistent >--verbose --unsafe qemu+ssh://root@172.31.255.11/system > How about using --xml to supply the destination XML which would have io="threads" specified? >error: unsupported configuration: native I/O needs either no disk cache >or directsync cache mode, QEMU will fallback to aio=threads > >This error persists even if the VM config file is changed to use >"io=threads". Of course, the running image continue to have "io=native" >on its parameters list, but it does not really honor the "io=native"...

Hi, I am trying to use libvirt with sheepdog. I am using Debian 8 stable with libvirt V1.21.0 I am encountering a Problem which already has been reported. ================================================================= See here: http://www.spinics.net/lists/virt-tools/msg08363.html ================================================================= qemu/libvirtd is not setting the path

...that because Qemu use write-back flag to open disk images by default. > so I hope to use O_DIRECT to avoid meeting that problem, but I'm failed under Xen platform with Qemu upstream. cache=none does not eliminate the need for flush. If you want to do that, try cache=writethrough or cache=directsync. Regarding the EFAULT you are seeing, did you check if the I/O buffer address is valid? Try breaking in gdb and inspecting /proc/<pid>/maps or just x <buffer-address> in gdb to see if the buffer is readable. Stefan _______________________________________________ Xen-devel mailing li...

Update: Using mount (read-only) and unmount commands in a script that loops continuously, we are able to see near instantaneous file modifications (less than 0.5 sec) performed on a Win7 live guest. We have to use the sync.exe utility (technet.microsoft.com/en-us/sysinternals/bb897438.aspx), otherwise changes are not visible for 10-20 sec. We tested sync.exe with our libguestfs test program

...39;m >> not sure what is the best in this case. >> >> Regarding disk, since it's LVM I've chosen to go to cache mode none and IO mode native. Also >> here cannot judge what's the best setup for the workload. I'm undecided to use IO mode threads >> along directsync cache mode. >> >> Finally I've set "ionice -c 1 -p <qemu-pid> -n 0" and "renice -n -10 <qemu-pid>" for the interested >> VM that I want to get best performance possible. >> >> Even with the above setup, the MSSQL VM has performance s...

...hard disk to flush its cache. libguestfs used sync(2) to force changes to disk. We didn't expect that qemu was caching anything because we used 'cache=none' for all writable disks, but it turns out that qemu creates a writeback cache anyway when you do this (you need to use 'cache=directsync' when you don't want a cache at all). (2) qemu's qcow2 disk cache code is buggy. If there are I/Os in flight when qemu shuts down, then qemu segfaults or assert fails. This can result in unwritten data. Unfortunately libguestfs ignored the result of waitpid(2) so we didn't see th...

What are the recommendations for running KVM images on BTRFS systems using kernel 3.4?  I saw older posts on the web complaining about poor performance, but I know a lot of work has gone into btrfs since then.  There also seemed to be the nocow option, but I didn''t find anything that said it actualy helped. Anybody have ideas? Thanks, Matt -- To unsubscribe from this list: send the line

...d file use 'file' as IDE hard disk 2/3 image -cdrom file use 'file' as IDE cdrom image (cdrom is ide1 master) -drive [file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i] [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off] [,cache=writethrough|writeback|none|directsync|unsafe][,format=f] [,serial=s][,addr=A][,id=name][,aio=threads|native] [,readonly=on|off][,copy-on-read=on|off] [[,bps=b]|[[,bps_rd=r][,bps_wr=w]]][[,iops=i]|[[,iops_rd=r][,iops_wr=w]] use 'file' as a drive image -set group.id.arg=value set &lt...