[OpenAFS] All limitations of OpenAFS

Lars Schimmer l.schimmer@cgv.tugraz.at
Tue, 26 Jan 2010 16:59:00 +0100

Hash: SHA1

Harald Barth wrote:
>> - -max number of db servers in one cell?
> I have seen cells with up to 7 db servers. Most cells use 3. A few use =

I know that 3 db servers are fine to work with.
But I do not know the exact size and setup of the cell - maybe it could
be handy to setup a db server on every fs, to.
And as the cell is planned in the 20-200 fileservers area, I just asked.
I would love to have 3-5 db servers distributed and fileservers
seperate, but money and other limitations could force me...

> I don't understand why you would want more than say 3. If you have
> unreliable network connections (say between Asia and South America)
> you should rather consider making more cells than one spanning the
> whole area with the bad network bottleneck in the middle. Here "good"
> is not bandwidth but good uptime, low packet drop and reasonable
> roundtrip times (multiple satelite hops are bad).
>> For a new EU project
> Oh, the fun!
> Which limitations are you most concerned about? What our users hit by
> in the past and what we had the most difficulty to work around are:
> - -max 64k slots for filenames in one directory
> - -software assuming that setuid(4711) is the sole thing needed to
>    access all files of user with uid 4711 for all future.

In this particular case there are some limitations:
- -old crypt of data transport (IMHO solved with new krb5)
- -limitations of fileservers COULD be reached (more than 256 sites in EU=
- -max numbers of files per directory for a "quick and dirty" user (lets
treat it like a usual harddrive)
- -max length of volname shows some problems on howto organize the volume=
- -group limitations per directory - plans are up to 50+ groups per
fileserver - hence the questions about limits on group-ACLs per directory

Our setup would look like:
1 cell EU wide, with 5-200+ local sites, each has at least one fileserver.
Each site has groups AKA departments.
Each group has special volumes on "its local" fileserver and on other
fileservers RO/RW rights to special directories/volumes.

(setup is guided by the rule "data HAS to be kept local and only local
groups and external persons with special rights should be able to read
it. Local groups should be able to make only very small subpart of data
available to one or more other (external) groups).

Another limit is the missing "alternate datastream" option, like NTFS in
Win7. As we plan to save some data and metadata into OpenAFS, alternate
datastreams would be nice (to save metadata beside the datafile).
Jeffrey already has some ideas about that problem, but we need to look
into our budget and you know...

> Harald.

Lars Schimmer
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