[Sheepdog] Sheepdog cluster expansion

[Fernando Frediani (Qube)]

Thanks Kazutaka, make sense.

So as long I keep my nodes either with the similar logical partition size or same individual disk sizes should be fine.

Does running more individual sheepdog daemons use much extra memory or isn't something to concern about really ?

Fernando

-----Original Message-----
From: MORITA Kazutaka [mailto:morita.kazutaka at lab.ntt.co.jp] 
Sent: 03 August 2011 09:59
To: Fernando Frediani (Qube)
Cc: 'sheepdog at lists.wpkg.org'
Subject: Re: [Sheepdog] Sheepdog cluster expansion

At Mon, 1 Aug 2011 14:46:20 +0000,
Fernando Frediani (Qube) wrote:
> 
> Hi Kazutaka,
> 
> So if eventually I add a new node which doesn't have the same size as the others (say 5TB) the maximum data to be stored will be 8.3TB per node ? If so than I risk my 5TB node run out of space ? Or 5TB will be the limit of data that I will be able to store on each of my 10TB nodes ?
> I mean in short what happens or what are my limits with a 3 nodes configuration 10TB+10TB+5TB.

The 5 TB disk will be the limit.  The data will be distributed uniformly, so in the above case, the maximum data size you can store would be about 15 TB (each disk has about 5 TB).

> 
> I guess I workaround for this is run a sheepdog process for each disk, but that would be fairly more complex and eventually use more Ram memory ? Thinking about a server with 24 disks.
> What you suggest in a scenario like this ?

Running a sheepdog daemon for each disk also had a problem; to handle node failure, replicated data shouldn't be stored to disks on the same node.

I've just sent a patch to support location-aware data placement.  This patch can ensure that replicated data is stored on different machines.
With this patch, I think it would work fine to run multiple sheep daemons on each server.


Thanks,

Kazutaka

> 
> For the last question I think it is somehow related to the first one. If eventually I add a node with enough disks for the OS+KVM and some small storage(say 2 disks, so 500GB) just to run the run the sheepdog process I would run in a worst scenario as described below ?
> 
> Thanks
> 
> Fernando
> 
> -----Original Message-----
> From: MORITA Kazutaka [mailto:morita.kazutaka at lab.ntt.co.jp]
> Sent: 01 August 2011 13:44
> To: Fernando Frediani (Qube)
> Cc: 'sheepdog at lists.wpkg.org'
> Subject: Re: [Sheepdog] Sheepdog cluster expansion
> 
> At Mon, 1 Aug 2011 08:44:15 +0000,
> Fernando Frediani (Qube) wrote:
> > 
> > Hi,
> > 
> > If I start my cluster with the following scenario: 2 Servers with 10TB each (one single logic drive presented by the Raid controller) and obviously copies=2 how should I grow it ?
> > 
> > Should I always add a 2 x Servers of 10TB every time I need to increase my storage or can I just do one by one and it will always balance the data between any number of servers available ?
> 
> You can add one by one.  The data will be balanced automatically without any configuration.
> 
> > 
> > If I can add one by one does these servers need always to be the exactly same size of others (10TB) or there is some flexibility on having a mixture of that and again the things will balance fine ?
> 
> Sheepdog assumes that all the disks have the same free space, so the data will be balanced uniformly even if there is a much larger disk.
> It is not impossible to handle different sized disks, but it is one of the future works.
> 
> > 
> > In another slightly different scenario if I have already enough storage for my KVM Virtual Machines and all I need is just CPU and Memory is it OK jus to add a node with that but without storage and make it use the sheepdog for its VMs as well ?
> 
> Basically, Sheepdog needs a local disk to use for a storage system.
> Though your VMs can connect to the other machine from out side of Sheepdog, in that case the connected server (gateway) could be a single point of failure.  The connection failover is also one of TODO items.
> 
> Thanks,
> 
> Kazutaka
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