Ah-ha, that would certainly explain what I'm seeing. Thank you István! :-)
Can anyone comment on how or where I can slip extra mount options into the proxmox hosts? I notice my /etc/fstab doesn't list the NFS mounts. Also, would there be any mileage in documentation warning that the "writethrough" option won't operate as expected if the underlying storage is over NFS? Cheers, Chris -----Original Message----- From: Pongrácz István [mailto:[email protected]] Sent: 04 February 2014 15:31 To: Chris Murray; Alexandre DERUMIER Cc: pve-user pve.proxmox.com Subject: RE: [PVE-User] Understanding write caching in proxmox You should: - force your server to export in sync mode - force your client to mount in sync mode From the nfs manpage: The NFS client treats the sync mount option differently than some other file systems (refer to mount(8) for a description of the generic sync and async mount options). If neither sync nor async is specified (or if the async option is specified), the NFS client delays sending application writes to the server until any of these events occur: Memory pressure forces reclamation of system memory resources. An application flushes file data explicitly with sync(2), msync(2), or fsync(3). An application closes a file with close(2). The file is locked/unlocked via fcntl(2). In other words, under normal circumstances, data written by an application may not immediately appear on the server that hosts the file. If the sync option is specified on a mount point, any system call that writes data to files on that mount point causes that data to be flushed to the server before the system call returns control to user space. This provides greater data cache coherence among clients, but at a significant performance cost. Good luck! ----------------eredeti üzenet----------------- Feladó: "Chris Murray" [email protected] Címzett: "Pongrácz István" , "Alexandre DERUMIER" [email protected] CC: "pve-user pve.proxmox.com" Dátum: Tue, 4 Feb 2014 14:58:06 -0000 ------------------------------------------------- > I'm not sure I get a chance to specify? > > root@pm02 :/# mount -l | grep 231 > 192.168.0.231:/mnt/foxpool on /mnt/pve/foxpool type nfs > (rw,relatime,vers=3,rsize=65536,wsize=65536,namlen=255,hard,proto=tc > p,timeo=600,retrans=2,sec=sys,mountaddr=192.168.0.231,mountvers=3,mo > untport=918,mountproto=udp,local_lock=none,addr=192.168.0.231) > > It was set up using the web interface, where I can't see an option for this. > > NFS client certainly feels asynchronous to me. Suppose I "sar -n DEV 1 | grep > eth0" > while I observe this 'buffering' effect ... I see next to no activity until > the > instant that "zpool iostat" does. i.e. the proxmox host is holding onto data > and > choosing to flush it at a later stage. > > Thanks again, > Chris > > -----Original Message----- > From: Pongrácz István [mailto:[email protected] ] > Sent: 04 February 2014 14:39 > To: Chris Murray; Alexandre DERUMIER > Cc: pve-user pve.proxmox.com > Subject: Re: [PVE-User] Understanding write caching in proxmox > > > How about your NFS setup? Sync, async? > > István > > ----------------eredeti üzenet----------------- > Feladó: "Chris Murray" [email protected] > Címzett: "Alexandre DERUMIER" [email protected] > CC: [email protected] > Dátum: Tue, 4 Feb 2014 14:14:51 -0000 > ------------------------------------------------- > > >> Sorry, I might have misled you with my question. It might have the >> appearance of another general and possibly quite common one. >> >> My troubleshooting was performed on the proxmox *host*, therefore I >> was under the impression that cache=[whatever] wouldn't make a >> difference since that's a property of a virtual machine disk. >> >> For the *VM*, I'm using writethrough .. however I'm observing exactly >> what you explained for 'none' or 'writeback'. My VM is Windows Server >> 2008 R2, and I'm using sdelete to fill it with data. 'sdelete -z' >> won't appear on the 'zpool iostat' for quite some time, while the >> cached figure on the proxmox host increases. That's despite the disk being >> set to writethrough. >> >> Apologies if I'm not being clear. >> > > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2014.0.4259 / Virus Database: 3684/7058 - Release Date: 02/03/14 > ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4259 / Virus Database: 3684/7058 - Release Date: 02/03/14 _______________________________________________ pve-user mailing list [email protected] http://pve.proxmox.com/cgi-bin/mailman/listinfo/pve-user
