[PVE-User] Understanding write caching in proxmox

[Pongrácz István]

 Hi,

Check your storage config file here:

/etc/pve/storage.cfg

Modify (add) your preferred switches to your nfs mount options. 
You can search the forum (or google) for examples if you are unsure.


I hope it solves your problem :)

Bye,
István

 
----------------eredeti üzenet-----------------
Feladó: "Chris Murray" chrismurray84 at gmail.com 
Címzett: "Pongrácz István" 
, "Alexandre DERUMIER" aderumier at odiso.com 
CC: "pve-user pve.proxmox.com" 
Dátum: Tue, 4 Feb 2014 16:01:58 -0000
-------------------------------------------------
 
 
> 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:pongracz.istvan at gmail.com ] 
> 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" chrismurray84 at gmail.com 
> Címzett: "Pongrácz István" 
> , "Alexandre DERUMIER" aderumier at odiso.com 
> 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 at 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:pongracz.istvan at gmail.com ] 
>> 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" chrismurray84 at gmail.com 
>> Címzett: "Alexandre DERUMIER" aderumier at odiso.com 
>> CC: pve-user at pve.proxmox.com 
>> 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.
>>> 
>> 
>> 
>> 
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> 
> 
> 
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