JBOD disk failure and lost items

Question

Dear.
We have a JBOD solution with 4 copies. Each copy is on a non-redundant disk.
For SMTP, the transport database has a shadow transport database and shadow safetynet on another server, which makes sure that a message isn’t lost in the event of a database crash at the moment that the SMTP message is being written to the database.
Is there some protection mechanism for MAPI or when an Outlook client is writing a contact or a meeting appointment a few seconds before the crash? I suppose that the appointment has been lost
because it’s not yet replicated to the copy databases?
Or, is there some end-to-end mechanism that returns the Outlook client that the appointment has been saved only when it’s already replicated to a copy database?
Thanks for the feedback.
Regards.
Peter
Peter Van Keymeulen, IT Infrastructure Solution Architect, www.edeconsulting.be

Answer 1

I found the following about the Block Mode replication:
"In block mode, as transactions are written into the ESE log buffer (the 1 MB cache used to accumulate transactions to be written into a transaction log), the log copier copies the data asynchronously (effectively in
parallel) to all the servers that hold a database copy. The data are written into a similar log buffer on these servers.
When the log buffer on the receiving servers is full, the complete buffer is written out as a transaction log. The new log is inspected to ensure that it is not corrupt, and if this check passes, the log is inserted into the
log stream to be replayed into the pas­sive database."
So, can we decide that, in block mode, each change on the active database comes into the log buffer (in memory) and directly copied to the log buffer on the copy servers? The log copier copies the data from the source buffer directly to the receive buffer,
in real time. When the receive buffer reaches a 1 MB size, it writes a transaction log file that will be inspected and processed. This means that we potentially can lose data of a few milliseconds only?
Peter Van Keymeulen, IT Infrastructure Solution Architect, www.edeconsulting.be