RE: Consistency checking in HA solutions

> From: jt
> Sent: Thursday, November 13, 2003 1:53 PM

> I guess my question would be, have you Ever found a block that was not in
> sync.  (If the two computer systems ever did get outta sync, finding out a
> couple weeks later would be rather unfortunate, imo/o
> (opinion/observation).)
>
>
> | -----Original Message-----
> | From: Sean Porterfield
> | Sent: Wednesday, November 12, 2003 9:24 AM
>
> | > Only problem is that only file/objects attributes are checked
> | (for example
> |
> | > What do other HA-Tools offer to check if the data on the backup
> | system is
> |
> | We're using Vision Solutions which offers a CRC Sync check as
> well as the
> | attribute check that you mentioned.  It checks the data in blocks of
> | records.  If any particular block is not in sync, we just send that one
> | block instead of the whole file.
> |
> | (This feature is one of the main reasons we chose Vision for HA.)
> |
> | HTH
>
> Yes, it is interesting discussion (imo)!


Is this directed at me?  I don't follow well once it's been top posted...
(I still read top to bottom for some strange reason ;) )

I'll answer anyway.  Yes, we have found data out of sync, but generally the
objects have already been put on hold because they failed the automatic
check.  We run the CRC check then fix the parts that fail.  We haven't taken
the time yet to figure out all of the reasons for objects to fail the check,
but the most common is when something unusual happens (like someone did a
CPYF *REPLACE or ended journaling or got a lock on the file on the target.

Unlike the other person who commented, we haven't run a full CRC check of
all files.  We are not 24x7 and still shut our system down for backup every
night; therefore, we cannot just let the CRC checks run for a couple days.

The truth is, if a fail passes the attribute check, it's unlikely to fail
the CRC check.  Yes, it can happen.  I won't quote a statistic (we all know
the value of them!) but Vision said they had a very high percentage of
success with the regular check.

As usual, YMMV.