[169299] in North American Network Operators' Group
Re: VMware Training
daemon@ATHENA.MIT.EDU (Dan Shoop)
Thu Feb 20 14:50:19 2014
From: Dan Shoop <shoop@iwiring.net>
In-Reply-To: <CAAAwwbX_Dy68OUmcLiqZ1RXoLdPgszo9Xm2nhiV14_06M9Mk0w@mail.gmail.com>
Date: Thu, 20 Feb 2014 14:49:25 -0500
To: Nanog <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Feb 20, 2014, at 1:48 PM, Jimmy Hess <mysidia@gmail.com> wrote:
> The locking restrictions are for your own protection. If the =
filesystem
> inside your virtual disks is not a clustered filesystem;
> two instances of a VM simultaneously mounting the same NTFS volume =
and
> writing some things, is an absolute disaster.
>=20
>=20
> Under normal circumstances, two applications should never be writing =
to
> the same file. This is true on clustered filesystems.
> This is true when running multiple applications on a single computer.
Why should "two applications should never be writing to the same file"? =
In a real clustered *file*system this is exactly what you want. The same =
logical volume mounted across host cluster members, perhaps geodistantly =
located, each having access at the record level to the data. This =
permits HA and for the application to be distributed across cluster =
nodes. If a host node is lost then the application stays running. If the =
physical volume is unavailable then logically shadowing the volume =
across node members or storage controllers / SANs permits fault =
tolerance. You don=92t need to =93fail disks over=94 (really logical =
volumes) as they are resilient from the start, they just don=92t fail. =
When the shadow members return they replay journals or resilver if the =
journals are lost.=20
I=92d note that this can be accomplished just so long as you have a =
common disk format across the OS nodes.=20
These problems were all resolved 40 years ago in mainframe and supermini =
systems. They=92re not new. VMware has been slowly reinventing =97 more =
accurately rediscovering =97 well known HA techniques as it=92s trying =
to mature. And it still has a lot of catching up to do. It=92s the same =
tale that microcomputers have been doing for decades as they=92ve come =
into use as servers.=20
However I=92m not sure what all of this has to do with network =
operations. ;)
-d=20
-----
Dan Shoop
shoop@iwiring.net
1-646-402-5293 (GoogleVoice)
