Hi,
Looks interesting.
On Tue, Aug 20, 2013 at 1:06 PM, Nulik Nol nulik...@gmail.com wrote:
Hi,
I am creating an email system which will handle whole company's email,
mostly internal mail. There will be thousands of companies and
hundreds of users per company. So I am planning to use one pool per
company to store email messages. Can Ceph manage thousands or maybe
hundred thousands of pools ? Could there be any slowdown at production
with such design after some growth?
You can't have thousands of pools. Each pool shows up in the OSDMap,
and each pool must have at least 1 pg. However, we now have rados
level namespaces which subdivide a pool. You can have as many
namespaces as objects if you want. The main caveat is that you can't
efficiently list the contents of a namespace. We do support user
capabilities on namespaces.
Every email will be stored as an individual ceph object (emails will
average 512 bytes and rarely have attachments) , is it ok to store
them as a ceph objects or will it be less efficient than storing
multiple emails in a ceph object,? What is the optimal ceph object
size to store individually, so it would be preferable to do this
instead of writing through omap with leveldb? (kind of ceph object vs
omap benchmark question)
I am unsure. Each rados object will end up as a file on the backing
filesystem, so there is some overhead there. My first instinct for
objects of 512 bytes might be to hash the key and use part of the
hash to determine the object name and the rest to determine the omap
key. It might be fine to do 1 email per object though.
Also I will be putting mini-chat sessions between users in a ceph
object, each time a user sends a message to another user, I will
append the text to the ceph object, so my question is, will Ceph
rewrite the whole object into a new physical location on disk when I
do an append? Or will it just rewrite the block that was modified?
Appends are performed using filesystem writes, so it won't overwrite
the entire object. Rados support partial overwrites just fine.
And last questions: Which is faster, storing small key/value pairs in
omap or in xattrs ? Will storing key/value pairs in xattrs result in
space waste by allocating a block for zero-sized object on the OSD? (I
won't write any data to the object, just use xattrs)
Depending on the backing filesystem, xattrs are either stored as xattrs
on the backing filesystem or as keys in leveldb (just like omap). I
suggest you reserve xattrs for small pieces of metadata and omap for
large sets of keys. zero sized objects are fine.
-Sam
Will appreciate very much your comments.
Best Regards
Nulik
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