active/active vs active/passive?

active/active vs active/passive?

[Dan Stromberg]

The lecturer at the recent NG storage talk at Usenix in Anaheim,
indicated that it was best to avoid "active/active" and get
"active/passive" instead.

Does anyone:

1) Know what these things mean?

2) Know why active/passive might be preferred over active/active?

If I had to guess, I'd say that active/active means that n servers are
all watching n-1 others to decide when they should jump to life, while
in active/passive perhaps 1 server is primary, and the passive nodes
only monitor that 1 server.  Maybe?  Just a totally wild guess based on
next to nothing.  :)

Thanks!

Re: active/active vs active/passive?

[Neil Brown]

On Tuesday June 7, strombrg@dcs.nac.uci.edu wrote:
> 
> The lecturer at the recent NG storage talk at Usenix in Anaheim,
> indicated that it was best to avoid "active/active" and get
> "active/passive" instead.
> 
> Does anyone:
> 
> 1) Know what these things mean?

There's not a lot of context, so it is hard to know.
Could be talking about multi-path devices.
e.g. you have two fibre-channel controllers which are each connected
to the same drive (or set of drives).  data/commands can be sent down
either channel to the drives.

active/active is where both (all) channels are actively in use (load
balancing?).
active/passive is where one is a warm-spare waiting to take over if
the active one fails.

> 
> 2) Know why active/passive might be preferred over active/active?

No idea.

NeilBrown

> 
> If I had to guess, I'd say that active/active means that n servers are
> all watching n-1 others to decide when they should jump to life, while
> in active/passive perhaps 1 server is primary, and the passive nodes
> only monitor that 1 server.  Maybe?  Just a totally wild guess based on
> next to nothing.  :)
> 
> Thanks!
> 
> 
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Re: active/active vs active/passive?

[Dan Stromberg]

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On Wed, 2005-06-08 at 10:16 +1000, Neil Brown wrote:
> On Tuesday June 7, strombrg@dcs.nac.uci.edu wrote:
> > 
> > The lecturer at the recent NG storage talk at Usenix in Anaheim,
> > indicated that it was best to avoid "active/active" and get
> > "active/passive" instead.
> > 
> > Does anyone:
> > 
> > 1) Know what these things mean?
> 
> There's not a lot of context, so it is hard to know.
> Could be talking about multi-path devices.
> e.g. you have two fibre-channel controllers which are each connected
> to the same drive (or set of drives).  data/commands can be sent down
> either channel to the drives.
> 
> active/active is where both (all) channels are actively in use (load
> balancing?).
> active/passive is where one is a warm-spare waiting to take over if
> the active one fails.

So it's basically trunking for performance vs. failover?
 
> > 
> > 2) Know why active/passive might be preferred over active/active?
> 
> No idea.

Gee, I sure wish I had more context on this.  I suspect it was something
he skipped past pretty quickly, and I was hard pressed to type
everything into my PDA.




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Re: active/active vs active/passive?

[Paul Clements]

Dan Stromberg wrote:
> The lecturer at the recent NG storage talk at Usenix in Anaheim,
> indicated that it was best to avoid "active/active" and get
> "active/passive" instead.
> 
> Does anyone:
> 
> 1) Know what these things mean?

In the clustering world, active/active means 2 or more servers are 
active at a time, either operating on separate data (and thus acting as 
passive failover partners to each other), or operating on the same data 
(which requires the use of a cluster filesystem or other similar 
mechanism to allow coherent simultaneous access to the data).

> 2) Know why active/passive might be preferred over active/active?

Well, if you're talking about active/passive vs. active/active with a 
cluster filesystem or such, the active/passive is tons easier to 
implement and get right. Plus, depending on your application, the added 
complexity of a cluster filesystem might not actually buy you much more 
than you could get with, say, NFS or Samba (CIFS).

--
Paul

Re: active/active vs active/passive?

[Dan Stromberg]

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On Tue, 2005-06-07 at 20:54 -0400, Paul Clements wrote:
> Dan Stromberg wrote:
> > The lecturer at the recent NG storage talk at Usenix in Anaheim,
> > indicated that it was best to avoid "active/active" and get
> > "active/passive" instead.
> > 
> > Does anyone:
> > 
> > 1) Know what these things mean?
> 
> In the clustering world, active/active means 2 or more servers are 
> active at a time, either operating on separate data (and thus acting as 
> passive failover partners to each other), or operating on the same data 
> (which requires the use of a cluster filesystem or other similar 
> mechanism to allow coherent simultaneous access to the data).

This is probably what the lecturer intended.

> > 2) Know why active/passive might be preferred over active/active?
> 
> Well, if you're talking about active/passive vs. active/active with a 
> cluster filesystem or such, the active/passive is tons easier to 
> implement and get right. Plus, depending on your application, the added 
> complexity of a cluster filesystem might not actually buy you much more 
> than you could get with, say, NFS or Samba (CIFS).

What it is about active/passive that is so much easier to implement than
active/active?

Thanks!


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Re: active/active vs active/passive?

[Paul Clements]

Dan Stromberg wrote:
> On Tue, 2005-06-07 at 20:54 -0400, Paul Clements wrote:

> What it is about active/passive that is so much easier to implement than
> active/active?

There's nothing that difficult about active/active, assuming you're 
talking about the servers operating on separate (or static) data. What's 
difficult is the cluster filesystem. Those tend to be big pieces of 
low-level (read, kernel) code, and they require a distributed lock 
manager and a membership model, which are also generally implemented 
in-kernel.

Of course, without knowing the context of the speaker's reference to 
this, it's hard to say exactly what he meant or if it's even remotely 
related to what I'm talking about... :)

--
Paul

Re: active/active vs active/passive?

[Dan Stromberg]

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On Wed, 2005-06-08 at 13:51 -0400, Paul Clements wrote:
> Dan Stromberg wrote:
> > On Tue, 2005-06-07 at 20:54 -0400, Paul Clements wrote:
> 
> > What it is about active/passive that is so much easier to implement than
> > active/active?
> 
> There's nothing that difficult about active/active, assuming you're 
> talking about the servers operating on separate (or static) data. What's 
> difficult is the cluster filesystem. Those tend to be big pieces of 
> low-level (read, kernel) code, and they require a distributed lock 
> manager and a membership model, which are also generally implemented 
> in-kernel.
> 
> Of course, without knowing the context of the speaker's reference to 
> this, it's hard to say exactly what he meant or if it's even remotely 
> related to what I'm talking about... :)

Is the difficulty mostly stemming from keeping stateful sessions and
content consistent across replica servers?


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Re: active/active vs active/passive?

[Paul Clements]

Dan Stromberg wrote:

> Is the difficulty mostly stemming from keeping stateful sessions and
> content consistent across replica servers?

Yes, that's it, more or less.

--
Paul

Re: active/active vs active/passive?

[Dan Stromberg]

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On Tue, 2005-06-07 at 17:09 -0700, Dan Stromberg wrote:
> The lecturer at the recent NG storage talk at Usenix in Anaheim,
> indicated that it was best to avoid "active/active" and get
> "active/passive" instead.
> 
> Does anyone:
> 
> 1) Know what these things mean?
> 
> 2) Know why active/passive might be preferred over active/active?
> 
> If I had to guess, I'd say that active/active means that n servers are
> all watching n-1 others to decide when they should jump to life, while
> in active/passive perhaps 1 server is primary, and the passive nodes
> only monitor that 1 server.  Maybe?  Just a totally wild guess based on
> next to nothing.  :)

I think I found a relevant context.  Say you have two RAID controllers
per "Storage Brick", the latter apparently being a dual-ported way of
accessing a SATA or FC disk.  Does active/active mean they'll send data
at the disk in question via both ports?

Thanks!


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