I worked with a similar EMC solution that you are talking about at my last
job. It worked pretty well for what we needed to do, however we did things
different then you are talking about
First, you are talking about splitting your BCV mirror every 30
minutes. You might want to look into that more because if I remember
correctly, our synchronize was taking over 2 hours. However, we needed to
attach broken mirrors every time. You might be able to make that time by
only needing to sync your changes (depending on how much you have going on
in the database).
Second, we always placed the database in backup mode whenever we split the
BCV. We used the archive logs to recover the dbfiles that were copied in
the split, just as if recovering from a hot backup. We sent continuos
copies of our archive logs over to the DR site along with the BCV split
site to do a recovery if it was needed.
We never went for the "one single atomic action", mainly because we just
never felt 100% comfortable with it. Add in the fact that there really is
no rolling forward if you are not placing the database in backup mode. If
you are only taking a snapshot every x minutes, x minutes of data loss is
guaranteed. As far as being certified by Oracle, our on site support said
no at the time. It is pretty much the same as taking a backup of a
database after a shutdown abort. It might work fine, just wasn't
supported/recommended by Oracle. Perhaps things have changed since then,
but I haven't heard that they have
Good luck
At 02:58 PM 3/24/2004 +0200, you wrote:
Lex,
It _is_ expensive. Of course this was advised by EMC. The first step was to consolidate three EMC Symmetrix boxes into one single 20 TB box.
That thing has three sets of disks: The normal mirrored set (2) and a BCV (the 3rd). The BCV acts as a second mirror. Every 30 minutes the BCV is split from the mirror, and all changed blocks are forwarded to the DR site some 70 miles away. Where, of course, a symmetric Symmetrix setup is needed. After sending the blocks, the BCV is added to the mirror again, synchronizes and it all starts over again. In the mean time, at the DR-site the normal mirror synchronizes with the BCV volume. Having all storage in one EMC box enables the EMC box to do the BCV-split in one atomic action.
This works in theory, and in most cases it will do so in practice as well. However, is there a situation this can be broken? I'm curious. If it breaks, it's probably due to a bug in the EMC-SW.
Another problem is that this setup will not recover from many human errors, like dropping a table or tablespace. On the contrary, TimeFinder will replicate the error flawless/flawfull (depending on the point of view) to the other end.
Mike's description pretty much covers the way Snapmirror of NetApp works. That does the same, but enables you to keep several snapshots on-line, thus enabling you to recover from a human error by activating the last snapshot before the problem, probably do a TSPITR and continue work. Falconsoft claims to have the same solution, HW-independent virtualizing the storage. I'm curious about real-life stories about that!
Regards, Carel-Jan
=== If you think education is expensive, try ignorance. (Derek Bok) ===
At 03:26 PM 3/24/2004, you wrote:Mike, Carel-Jan,
this sounds like a pretty expensive solution (and I am not talking money here) -- just imagine how many I/O activity you typically have against an online Oracle database... this means that after the "snapshot point in time" you basically start writing every block twice -- once to the database, and once to the snapshot.
well, I can tell you, the Oracle mechanism (activated by putting files in backup mode) is definitely cheaper, because it is a more intelligent algorithm; it only writes full block images to the redo log when needed for recoverability, and definitely NOT for every change ...
cheers, Lex.
-----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Michael Boligan Sent: woensdag 24 maart 2004 13:52 To: oracle-l@xxxxxxxxxxxxx Subject: RE: Falconstor/IPStor with Clariion, EMC Timefinder with Symmetrix
Carel-Jan,
We are looking at using Compaq's Virtual Snapshot Replicator for one of our Sqealserver databases. The way it works is that when you create a snapshot it creates a file which contains a pointer to the database file. When someone changes the database, the before image is written to the snapshot file. At this point the file is no longer just a pointer it containts before image data. The backup, will backup the snapshot, not the database file. This provides a consistent image. This is very different than EMC Timefinder, which is used to backup a mirrored database. When you break the mirror Timefinder ensures that no data is in the buffers that would make the mirrored data incomplete. At this point you can bring the mirrored database down and get a cold backup, then resync the mirrors. I have not used it so I can't give any feedback as to if it works as advertised or not. Timefinder is a better option, in my opinion, and more expensive. Snapshot replication is for the lower end disk arrays that can't provide anything like Timefinder because the array doesn't have an on board CPU.
HTH, Mike
|---------+-----------------------------> | | "Lex de Haan" | | | <lex.de.haan@natur| | | aljoin.nl> | | | Sent by: | | | oracle-l-bounce@fr| | | eelists.org | | | | | | | | | 03/24/2004 06:27 | | | AM | | | Please respond to | | | oracle-l | | | | |---------+----------------------------->
>--------------------------------------------------------------------------- --------------------------------------------| | | | To: <oracle-l@xxxxxxxxxxxxx> | | cc: | | Subject: RE: Falconstor/IPStor with Clariion, EMC Timefinder with Symmetrix |
>--------------------------------------------------------------------------- --------------------------------------------|
Carel-Jan,
the *one and only* reason why you need to put Oracle data files in backup mode is to avoid fractured blocks -- that is, ending up with Oracle blocks (spanning multiple OS blocks) with the header and footer out of sync. I don't know the technology of "snapshotting" all data files in a single atomic action -- sounds interesting to me... how do they do this? be careful, this might be marketing language, with some vipers under the grass ;-)
anyway, if it is really true that they can guarantee this "atomic snapshotting" you would be able to do hot backups without the need to put your tablespaces or data files in backup mode. By the way, you don't really need it at the database level; at the data file level it is good enough.
Whether this is supported, that's another story.
Cheers, Lex.
-----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Carel-Jan Engel Sent: woensdag 24 maart 2004 10:12 To: oracle-l@xxxxxxxxxxxxx Subject: Falconstor/IPStor with Clariion, EMC Timefinder with Symmetrix
Hi list,
Does anyone know these products for HA-solutions? Especially, is it possible/certified to snapshot databases without putting the database in backup mode?
The idea behind it is that all datafiles (incl. control and online redolog) are snapshotted in one single atomic action. The snapshot is stored at a local mirror, and asynchronously transferred to the DR-site. Failover can be performed by starting and (auto)recovering the database at the DR site. Because all files were copied in the state they were in one point in time, starting the database at the remote site should be the same as starting a database after a power failure.
I'm not interested in all kinds of other HA solutions, the site I'm currently working for has implemented these solutions, but needs verification. It's hard to get commitment from the vendors that their products are certified for Oracle, although they advised and sold the solution :-(.
Thanks, Carel-Jan
=== If you think education is expensive, try ignorance. (Derek Bok) ===
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