[AusNOG] Back of envelope II

[Nathan Gardiner]

VMWare ESX is an expensive way to achieve server redundancy, if that's
your only goal. SAN redundancy can be achieved through multipath on
linux with equivalent solutions on Windows. Network redundancy can be
achieved through bonding or teaming of NIC adaptors.

The equivalent of what you are achieving through virtualisation is
possible by deploying several hosts with the same function and using
content switches, or even OSPF/anycast, to allow a single node to be
taken down without (any/much) operational impact. Shared SAN storage
and clustered filesystems can allow several nodes (with the correct
application intelligence) to access the same data volumes.

Virtualisation works well and reduces cost, but is not without
limitation. High network utilisation can saturate shared network
connections, high CPU can cause latency across the host, high SAN
utilisation can cause storage latency. High memory utilisation can
cause swapping, which in turn causes significant latency. You can
always scale VMWare hosts but there is a cost involved - the higher
you scale to deal with infrequent utilisation, the less of an
advantage you gain by virtualising (not to mention licensing costs on
top).


Nathan

On Fri, Mar 6, 2009 at 1:34 PM, Skeeve Stevens <skeeve at eintellego.net> wrote:
> The ONLY solid way that I know to do good server redundancy is with Virtual Platforms that support SAN, Fibre Channel/iSCSI with diverse heads.
>
> We manage multiple instances of VMware ESX/ESXi that have 2+ heads backed into SAN's with both heads fed into Cisco switches - nearly always 3560G/3750G-stacked configurations.
>
> Those have never gone down, even when upgrading the physical hardware - VM's just migrate between heads.
>
> Some say VM's aren't appropriate for some applications... I would debate that as even in a dedicated VM solution there is not many apps that wouldn't happily work with that given dedicated NIC, Storage, CPU and RAM access.
>
> ...Skeeve
>
> --
> Skeeve Stevens, CEO/Technical Director
> eintellego Pty Ltd - The Networking Specialists
> skeeve at eintellego.net / www.eintellego.net
> Phone: 1300 753 383, Fax: (+612) 8572 9954
> Cell +61 (0)414 753 383 / skype://skeeve
> --
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>
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>
>> -----Original Message-----
>> From: ausnog-bounces at lists.ausnog.net [mailto:ausnog-
>> bounces at lists.ausnog.net] On Behalf Of Michael Bethune
>> Sent: Friday, 6 March 2009 12:14 PM
>> To: ausnog at ausnog.net
>> Subject: [AusNOG] Back of envelope II
>>
>> Thanks folks for all the responses.
>>
>> Is it possible to do auto fail over redundant switching and what if
>> anything
>> in the Cisco range would do it?
>>
>> I remember using a dual cisco catalyst, but you ended up with a pair of
>> tails, 1 from each catalyst, with a heart beat connecting the two
>> catalysts
>> together. Has the state moved on to allow you to have transparent (to
>> the
>> connected hosts) redundant switching?
>>
>> Michael.
>>
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