XP business copy "quick split" question.

[Anthony Kloppers_1]

I believe the default operation for business copy XP on the XP1024 is the quick split behaviour (settable via a mode switch). I know that the S-vol becomes available immediatly for read / write operations after the pair is suspended, even if the S-vol is not completely in sync with the P-vol. If the backup application needs to read a block on the S-vol that is out of sync with the P-vol, it gets the data from the P-vol instead. What happens now if a host attempts to write to a block on the P-vol that is not yet copied across to the S-vol, - is the host acknowledgement then delayed, or does the write just remain in cache until the particular block can be written to the P-vol? Any documents detailing this behaviour would be most welcome. The raid manager manual does not give too much info here. The reason this is important to know is this: At what stage is it safe to start writing to the P-vol after the pair is suspended? Is this immediatly when the P-vol is in P-sus state, or only when the S-vol is out of COPY state and in S-SUS state?

[Peter Mattei]

The XP arrays are all cache centric machines. All writes to an XP are acknowledged when they are in the battery backed write cache no matter if you are using BC or not.

It is always save to write to the P or S vol!
If you do not trust the XP availability features you would not use quick split at all!

For a detailed description read in chapter 23 of the Command View user guide. Here the quick split function is also called at-time split.

http://h200005.www2.hp.com/bc/docs/support/SupportManual/c00312425/c00312425.pdf

Cheers
Peter

[giuseppe monardo]

Hi at all,

I saw it's possible to have use at-time split or quick split, but I'm not so sure it's good for me.

We use business copy for backup, but our datawarehouse are in terms of 10TB. Once time a week, I resync the P-VOL and S-VOL, but this time can take 24hours or more, in some case. What I'd like is that P-VOL and S-VOL can resync immediately, so I can start up my DB. The question is: where the storage writes the delta tracks that are not sync ? How the S-VOL take the data from P-VOL, during the background process ? There is something like journal, pherhaps ? Somewhere, I have to write the delta tracks that are not sync when I create the at-time BC, it's right ?? And from performance side, how much it impacts on P-VOL or cache ??
I don't find any documents.

Thanks a lot

Dr.Ing. Monardo G.A.

[Alzhy]

Anthony,

Looks to me like you have doubts on the workings of the Hitachi technology in the XP1024 sir. Believe me -- it is ONE if tnot the most trusted HW based split mirror (aka BCV to the EMC folks) technologies around. I am quite puzzled by your concern at split time but hope this explanation makes it easy on ya sir:

At split time - the consistency of the SVOL data largely depends on how quiesced is the storage structure on top of the PVOL OR even how excellent the container (i.e. Filesystem) of data is on top of the PVOLs. In the case of Databases - Oracle needs to have the instance be in what is called Hot Backup State - where writes and updates to the DB are contained "somewhere else" and makes the main data consistent for a SPLIT. For modern filesystems -- like vXFS, NTFS, ext2/3/4, etc -- There WILL always be some need for those filesystems to be checked for consistency and open files or those that were in-flight will of course have some inconistencies -- so USAGE really is up to the end user.


And to Signori Mondardo:

If you have a 10TB Database and you use BizCopy on it with a synch of only once a week -- then that is practicaly doing a paircreate (or FULL synch) -- You need to review usage f BiZCopy then sir. It does not make sense to do it that way if you are using it as your main backup solution.

[giuseppe monardo]

Sorry, but I suppose it's one of few possible methods to backup a very large DB (we have several DB like this). Otherwise, I need a lot of drive to backup on tape. I can use snapshot, maybe, but I'm not so sure in terms of performance.
The question is: where my delta tracks are written if immediately P-VOL and S-VOL are in pair, after a quick split ?? Ok, the storage works in background, but somewhere the storage have to put the data, and in case of datawarehouse there are a lots of changing data !!

I need quick resync finally, but I suppose I can have quick resync only if I set quick split.

Thanks a lot

Dr.Ing. Monardo G.A.

[Alzhy]

Well -- we have DBs larger than that and what we do is do a synch nightly (prior to batch). We have deltas of an average of 12%. Doing so - we are assured we can fall back a DB to at least a full day back (and just apply archive logs if needed).

We also push the SVOLs to tape for off-sighting everyday -- of course on a separate server. We use LTO4 drives - 4Gbit drives where we average around 2TB per cartidge (compression).

Maybe you can also try hooking up some lower cost MSA SATA arrays or even EVAs to your XP via External Storage/XP and have your backups on them. 2nd Tier Storage (SATA/FATA) is cheap these days.. so lots of possibilities to provide backups to any mision critical database.

[Peter Mattei]

Hi Giuseppe

What XP are you talking about?
Not all features are available on older models.

And, Quick Split and Quick Restore are absolutely independend!

Regarding BC Split. Here some text out of the BC User Guide:

Four options are available when splitting a pair:
- Steady split, which is a typical pair split operation in which any remaining differential data from the P-VOL is copied to the S-VOL and then the pair is split.

- Quick split, in which the pair is immediately split so that the S-VOL is immediately available for read and write I/O. Any remaining differential data is copied to the S-VOL in the background.

- At-Time Split, in which all pairs in a consistency group are split at the same time. Split time indicates the time when you want to mirror P-VOL data in the S-VOLs. RAID Manager is required.

- Create and simultaneously split an L1 or L2 pair. This allows you to access S-VOLs as soon as possible

I suggest you download the BC User Guide from hp.com and search for "Quick".

Cheers
XP-Pete

[Alzhy]

Hitachi 99XX (aka XP1024)...
I guess no External Storage/XP here eh Petre?


Sirs -- I am passionate about hitachi technology that is why the myriad os suggestions on how to best utilize these storage frames. It always pains me whenever I hear/see such arrays ineffiently used. ;^(

[giuseppe monardo]

Sure I read the documentation, and is for that cause that I wrote on this forum, just because the documentation it's not so exhaustive.

My question is, I repeat, more on quick resync rather than quick split.
After a split (P-SUS and S-SUS), I need to resync immediately the two BC disk. On HITACHI Forum, I read that is possible to do "quick resync", but quick resync is just useful for script, because the P-VOL and S-VOL are in copy for all the period that needs a normal sync. But, however, the storage set the BC disk as "PAIR", but in background the copy are still in progress maybe. Finally, the BC disk are not really in PAIR for a long time (The time of "Normal" sync), but for the storage "GUI" or raidmanager it is as if they were.

About backup question, I use BC because I need a lot of LTO4 drives for backup a DWH of 10TB, and maybe (For a lot of problems) the job can fail.
6 days on week , the P-SUS and S-SUS remain in split (in case of restore I can mount the S-VOL), and once a week I've to resync the data because I need another backup.
After ish 24 hours, the P-VOL and S-VOL are in sync (after the pairresync operation, unfortunately too slow for me !!): at this point I stop my DWH (Datawarehouse) and I do pairsplit. Teen, I restart my DWH.
ON Saturday I start to resync P-VOL and S-VOL but sometimes the storage can't resync in 12 or 24 hours the data and I can't stop my DB where I want.

bye

[Peter Mattei]

Hi Guiseppe

Please do not get me wrong; all I want to do is understand your question and help.

I am still unsure what XP you are operating. Is it an XP1024 as Alzhy mentoned?

Unfortunately I am still not absolutely sure about the issue. I try to comment your last post a I understand it.

Guiseppe: After a split (P-SUS and S-SUS), I need to resync immediately the two BC disk. On HITACHI Forum, I read that is possible to do "quick resync", but quick resync is just useful for script, because the P-VOL and S-VOL are in copy for all the period that needs a normal sync. But, however, the storage set the BC disk as "PAIR", but in background the copy are still in progress maybe. Finally, the BC disk are not really in PAIR for a long time (The time of "Normal" sync), but for the storage "GUI" or raidmanager it is as if they were.

Pete: If you do a split followed by a resync there will not be much to copy, so the resync will be done very fast.

BTW - I have attached a nice flowchart of XP12000 BC operations. It may help understanding the flow.

Guiseppe: About backup question, I use BC because I need a lot of LTO4 drives for backup a DWH of 10TB, and maybe (For a lot of problems) the job can fail.
6 days on week , the P-SUS and S-SUS remain in split (in case of restore I can mount the S-VOL), and once a week I've to resync the data because I need another backup.
After ish 24 hours, the P-VOL and S-VOL are in sync (after the pairresync operation, unfortunately too slow for me !!): at this point I stop my DWH (Datawarehouse) and I do pairsplit. Teen, I restart my DWH.
ON Saturday I start to resync P-VOL and S-VOL but sometimes the storage can't resync in 12 or 24 hours the data and I can't stop my DB where I want.

Pete: Well, If the resync is not fast enough for your purpose, you need to have two Business Copies - one for your restore and one for your backup requirements.
You can then split and resync the two independent BC pairs at any time.

Did I get it right now?

Cheers
Pete

[Peter Mattei]

In addition I want to come back to one of your initial questions:

Guiseppe: The question is: where the storage writes the delta tracks that are not sync ? How the S-VOL take the data from P-VOL, during the background process ? There is something like journal, pherhaps ? Somewhere, I have to write the delta tracks that are not sync when I create the at-time BC, it's right ?? And from performance side, how much it impacts on P-VOL or cache ??

Pete: Each BC vol has a track map in Shared Memory where the XP records track changes.
When you split a pair a differential bitmap is created.

- If you update a track on the P-vol before the track has been copied to the S-vol the XP will first copy the track to the S-vol and then update the track on the P-vol.

- If you read a track from the S-vol that has not been copied it will be read from the P-vol.
You see, the XP can perfectly handle this.

These processes of course do have some performance impact. But since most BC tasks are performed asynchronously in the background they do usually not hurt that much.

Cheers
Pete

[giuseppe monardo]

We have XP24000 and P9500

I don't understand very much, maybe we have not centered my "FOCUS".

I just would like to understand if it's possible to do a QUICK PAIRRESYNC and if QUICK PAIRRESYNC is consistent (in other words, if P-VOL and S-VOL are consistent immediately after the quick pairresync, obviously when P-VOL and S-VOL are in PAIR state).
If I understood correctly from hitachi forum, for example, the storage shows me PAIR STATE faster than normal pairresync operation, but I see that it's a "fake" status, infact P-VOL and S-VOL are still in copy in backgroung.

What do you think about this ?

Thanks a lot in advance