SQL Server error/warning 825
Here you can find the explnation of this error by Paul Randal:
A little-known sign of impending doom: error 825

From SQL Server 2005 onwards, if you ever see an 823 or 824, SQL
Server has actually tried that I/O a total of 4 times before it
finally declares a lost cause and surfaces the high-severity I/O error
to the connection’s console, killing the connection into the
bargain. The idea behind this read-retry logic came from Exchange,
where adding the logic reduced the amount of immediate downtime that
customers experienced. While in concept this was something I agreed
with at the time, I didn’t agree with the way it was implemented.
If the I/O continues to fail, then the 823/824 is surfaced – that’s fine. But what if the I/O succeeds on one of the retries?
No high-severity error is raised, and the query completes, blissfully
unaware that anything untoward happened. However, something did go
badly wrong – the I/O subsystem failed to read 8KB of data correctly
until the read was attempted again. Basically, the I/O subsystem had a
problem, which luckily wasn’t fatal this time. And that’s what I
don’t like – the I/O subsystem went wrong but there are no flashing
lights and alarm bells that fire for the DBA, as with an 823 or 824.
If read-retry is required to get a read to complete, the only notification of this is a severity-10 informational message in the
error log – error 825.
Additional messages in the SQL Server error log and system event log may provide more detail. This error condition threatens
database integrity and must be corrected. Complete a full database
consistency check (DBCC CHECKDB). This error can be caused by many
factors; for more information, see SQL Server Books Online.
What this message is really saying is that your I/O subsystem is going wrong and you must do something about it. And unless you’re
regularly scanning the error log looking for these, you’ll be
none-the-wiser.