On Mon, Apr 24, 2017 at 1:24 PM, Gandalf Corvotempesta <gandalf.corvotempesta@xxxxxxxxx> wrote:
Il 24 apr 2017 9:40 AM, "Ashish Pandey" <aspandey@xxxxxxxxxx> ha scritto:There is difference between server and bricks which we should understand.When we say m+n = 6+2, then we are talking about the bricks.Total number of bricks are m+n = 8.Now, these bricks could be anywhere on any server. The only thing is that the server should be a part of cluster.You can have all the 8 bricks on one server or on 8 different servers.So, there is no *restriction* on number of servers when you add bricks. However, the number of bricks which you want to add should be in multiple of theconfiguration you have.This is clear but it doesn't change the resultAs no one is using gluster to replicate data by loosing redundancy (it's nonsense), adding bricks means adding serversIf our server are already full with no more available slots for adding disks, the only solution is to add 8 servers more (at least 1 brick per server)In you case it should be 8, 16, 24...."can I add a single node moving from 6:2 to 7:2 and so on ?"You can not make 6+2 config volume to 7+2 volume. You can not change the *configuration* of an existing volume.You can just add bricks in multiple to increase the storage capacity.Yes and this is the worst thing in gluster: the almost zero flexibility
Bigger the cluster, higher the cost to maintain it or expand it.
At least in case of EC it is with good reason. If you want to change volume's configuration from 6+2->7+2 you have to compute the encoding again and place different data on the resulting 9 bricks. Which has to be done for all files. It is better to just create a new volume with 7+2 and just copy the files on to this volume and remove the original files on volume with 6+2.
If you start with a 6:2 by using commodity hardware, you are screwed, your next upgrade will be 8 servers with 1 disk/brick each.
Not true.
Yes, gluster doesn't make use of any metadata server, but I really prefer to add 2 metadata server and 1 storage server at once when needed than avoid metadata servers but being forced to add a bounch of servers every timeMore servers means more power cost, more hardware that could fails and so on.Let's assume a replica 3 cluster.If I need to add 2tb more, I have to add 3 servers with 2tb on each server.Ceph, Lizard, Moose and others allow adding a single server/disk and then they rebalance data aroud by freeing up the used space adding the new disk.
Didn't understand this math. If you want to add 2TB capacity to a volume that is 3-way replicated, you essentially need to add 6TB in whatever solution you have. At least 6TB with a single server. Which you can do even with Gluster.
I thought that this lack of flexibility was addressed is some way in latest version...
I think we had this discussion last July[1] with you that we can simulate the same things other storage solutions with metadata do by doing replace-bricks and rebalance. If you have a new server with 8 bricks then we can add a single server and make sure things are rebalanced with 6+2. Please note it is better to use data-bricks that is power of 2 like 4+2/8+2/16+4 etc than 6+2.
Are you suggesting this process to be easier through commands, rather than for administrators to figure out how to place the data?
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Pranith
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