[Gluster-users] distribute replicated volume and tons of questions
joe at julianfamily.org
Wed Feb 22 18:27:51 UTC 2017
On 02/21/17 09:33, Gandalf Corvotempesta wrote:
> Some questions:
> 1) can I start with a simple replicated volume and then move to a
> ditributed, replicated by adding more bricks ? I would like to start
> with 3 disks and then add 3 disks more in next month.
> seems stupid but this allow me to buy disks from different production batches.
Yes, you'll need to rebalance after you add a dht set so the hash table
can utilize the new subvolume(s).
> 2) let's assume (to keep it simple) a 1GB file with sharding enabled
> with 100MB size.
> In a replicated volume with just 1 replicated brick, all shared (and
> thus the file) are placed on the brick (replicated to 3 servers).
> What in case of 2 bricks ? Gluster will place shard 1 to 5 on brick1,
> and 6 to 10 on brick2 or "distribution" only happen for the whole file
> ? (in example, all shards for file1 are placed on brick1, and all
> shards for file2 are placed on brick2)
My understanding is that the shards will be distributed using the same
distributed hash table algorithm as any other file. (See
> 3) Based on question 2, when accessing a distributed file, gluster
> will read from all disks increasing the available bandwidth and
> thourhgput ?
That depends on where your bandwidth bottlenecks are.
> 4) Still keeping it simple, very simple: let's assume a VM with 10GB
> disk image placed on a distributed replicated volume. This VM hosts a
> simple webserver with a simple, but huge, website.
> Users accessing the website will access different section of the
> underlaying disk image.
> These accesses are distributed across the 2 bricks doubling the read
> performance (and write performance, as I can write on 2 disks at once)
If your web servers are hitting the disk for every page load, you're
doing it wrong. As for your performance question, you are on the right
train of thought.
> 5) by using ZFS, should I use a redundant ZIL ? What happens in case
> of ZIL failure? Usually, some date are lost, but Gluster is replicated
> in a syncronous way, thus loosing a ZIL on a single server should not
> be an issue, right ? Is gluster able to recover from this
> automatically ?
I can't answer ZFS questions. I, personally, don't feel it's worth all
the hype it's getting and I don't use it.
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