[Samba] sizing samba environment

[Meike Stone]

Hello,

I like migrate and consolidate a lot of Windows and samba files
servers to a new samba installation.

Following situation:
----------------------
At the moment are working about 3000 users in two sites with a amount
of 30TB data.
Over the next years, it may grow up until 50TB data volume.

Planned Hardware:
----------------------
The new disk storage is connected via FC (8GBit/s) to a site redundant
SAN. The storage itself uses a online mirror. Planned at the moment is
to use 4 servers (two Servers at each site) with each 64GByte RAM and
2x Intel Xeon E5-2630 V2 (6 cores each).

Planned configuration:
----------------------
Shares are distributed over all 4 servers. In disaster case (one site
is offline) the remaining site
must be capable to handle the shares/users from the other site
(reduced speed is acceptable).
Each samba Server gets a VIP, in disaster case, the VIP and the
storage mounts will be manual (scripted) moved to the servers on the
other site (I don't want using HA with CTDB, OpenAIS/Corosync,
Pacemaker, OCFS2, ...).
The samba servers are configured as "virtual server" as described in
https://www.samba.org/samba/docs/man/Samba-HOWTO-Collection/cfgsmarts.html
So each server gets (almost) the same configuration.
For decrease the recover time (fschk , date restore from backup), the
idea is, to split the directory configured in  "share path" into
different mount points (partition) in "smaller" volumes like 3-5TB.
Additional advantage is, that if one file system crashes, not all data
is impacted...

My Questions:
----------------------
Are there any sizing guides around there or does anyone can help me?

I need help to make the decisions like:

* What file system is suitable. I think about ext4 or xfs.
(stability/reliability, time for fschk, speed of file system)

* What max size is a acceptable for the file system?

* Sizing of Server(s)
- How many RAM must I size for one user?
- How many servers/cores should I use?

* is it recommended or a good idea to use LVM?
* is vfs_shadow_copy2 a good solution to provide snapshots to the
windows clients in such environment?
  (I'm too timid to use btrfs ...)


 Thanks for helping  Meike