The client does a 12MB read, which (because of the striping)
gets broken into 3 separate 4MB reads, each of which is sent,
all in parallel, to 3 distinct OSDs. The only bottle-neck
in such an operation is the client-NIC.
On 04/16/2013 01:06 PM, Gandalf Corvotempesta wrote:
2013/4/16 Mark Kampe <mark.kampe@xxxxxxxxxxx>:
RADOS is the underlying storage cluster, but the access methods (block,
object, and file) stripe their data across many RADOS objects, which
CRUSH very effectively distributes across all of the servers. A 100MB
read or write turns into dozens of parallel operations to servers all
over the cluster.
Let me try to explain.
AFAIK check will split datas into chunks of 4MB each, so, a single
12MB file will be stored in 3 different chunks across multiple OSDs
and then replicated many times (based on value of replica count)
Let's assume a 12MB file and a 3x replica.
RADOS will create 3x3 chuks for the same file stored on 9 OSDs
When reading AFAIK replicas are not used, so all reads are done to the
"master copy".
But these 3 chunks are read in parallel on multiple OSDs or all read
request are done trough a single OSD? In the first case we will have
3x bandwidth for read operations directed to a file with at least 3
chunks, in the latter we have a big bottleneck.
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