Large volumes

[Craig_Everhart@transarc.com]

Excerpts from transarc.external.arla-drinkers: 12-Dec-01 Re: Large
volumes David M. Karlsen at davidka (1899*)

> Hm, am I missing someting here.

> Scenario I: To volumes of 10 GB each. 1 GB changes on both volumes. The 
> outage occurs. Server is back. Replication starts on vol1 and vol2.

> Scenario II: One volume of 20GB, 2 GB changes. Outage occurs. Server 
> back. Replication of 2 GB of vol1 starts.

> Same time - same files - same problems? The thing is: I may want 
> directories bigger than 8GB (all the 8GB in one dir - no subdirs) - so 
> making multiple volumes is not an option.

Imagine that there's a network failure after shipping 1.3GB, and 20
minutes later it's back.  Scenario I: vol1 had already finished, so only
vol2 needs to be shipped.  Scenario II: vol1 has to be replicated from
scratch.


> >By the way, you might want to reconsider the second level of your tree
> >under /afs; it's conventional to put a cell name there so that you might
> >someday be able to deal with multiple cells.
> >
> ah -yes - the domainname by convention. Is OpenAFS in the same state as 
> CODA - allowing a client to belong to one, and only one, cell at a time?

> /afs/mydomain.com/data1
> /afs/mydomain.com/data2

> where data1 needs to hold over 10Gb. (More like 60GB)

An AFS client doesn't really belong to a cell.  An AFS file belongs to
exactly one cell.

> >>that's why I want to go for one big volume: /afs/data
> >>
> >
> >It's far less failure-prone to have many smaller volumes.  Remember that
> >you'll replicate the mount points as you replicate the parent volumes,
> >so that you *will* have multiple copies of the same stuff.
> >
> Yeah - that's my goal for the cluster  - so if one server fails - my 
> services (and their data) will continue to serve.

> Why I want large vols:
> -less administration
-need for many large files within the same directory

I can't help with the many files within a single directory, except to
wonder if that's strictly necessary.  If it were a good idea to put lots
and lots of files in one directory, some of them might be symlinks.

AFS has some hard limitations, though.  Directories themselves can be
only 2 MB in size, which makes for something like an 8k-file maximum, or
maybe 16K files if the names are small.  Also, AFS can't deal with files
over 2GB in size.  These limitations are present in OpenAFS as well,
though there is some work that I think is in progress to work with
larger single files.

		Craig