On 01/16/2013 03:46 PM, Sage Weil wrote:
On Wed, 16 Jan 2013, Gandalf Corvotempesta wrote:
2013/1/16 Sage Weil <s...@inktank.com>:
This sort of configuration effectively bundles the disk and SSD into a
single unit, where the failure of either results in the loss of both.
From Ceph's perspective, it doesn't matter if the thing it is sitting on
is a single disk, an SSD+disk flashcache thing, or a big RAID array. All
that changes is the probability of failure.
Ok, it will fail, but this should not be an issue, in a cluster like
ceph, right?
With or without flashcache or SSD, ceph should be able to handle
disks/nodes/osds failures on its own by replicating in real time to
multiple server.
Exactly.
Should I worry about loosing data in case of failure? It should
rebalance automatically in case of failure with no data loss.
You should not worry, except to the extent that 2 might fail
simultaneously, and failures in general are not good things.
I would worry that there is a lot of stuff piling onto the SSD and it may
become your bottleneck. My guess is that another 1-2 SSDs will be a
better 'balance', but only experiementation will really tell us that.
Otherwise, those seem to all be good things to put on teh SSD!
I can't add more than 2 SSD, I don't have enough space.
I can move OS to the first 2 spinning disks in raid1 software, if this
will improve performance of SSD
What about swap? I'm thinking to no use swap at all and start with
16/32GB RAM
You could use the first (single) disk for os and logs. You might not even
bother with raid1, since you will presumably be replicating across hosts.
When the OSD disk dies, you can re-run your chef/juju/puppet rule or
whatever provisioning tool is at work to reinstall/configure the OS disk.
The data on the SSDs and data disks will all be intact.
Other options might be network boot or even usb stick boot.
sage
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