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I am reviewing an Oracle XtremIO white paper and came across the statement..
"when you have to copy a closed redo log file to the archived destination, the operation is completed instantly. The operation remains a foreground-copy operation, therefore, the array does not perform actual physical I/Os to the back end; instead, it sends updates to in-memory pointers."
My question is simple: is this correct?
jeff_browning
256 Posts
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February 7th, 2014 06:00
OK, I took a look at this. What the document is saying is not only applicable to an archived redo logfile. Oracle simply does a physical copy of the online redo log file, obviously. It is in the nature of dedupe that when a physical file is copied, all of the blocks are deduped by definition. Therefore, as the doc says, the copy operation completes very quickly. (Nothing is truly instant, obviously, but it is much faster than a copy to mechanical disk.) And, yes, the entire copy operation occurs in memory and uses back end pointers only. No new data blocks in other words.
jeff_browning
256 Posts
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February 7th, 2014 06:00
Great question, Sam. Let me have a look.
zhaos2
643 Posts
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February 7th, 2014 19:00
Agree with Jeff, it is actually a point-in-time snapshot with pointers, not actual data copy. That is the way how XtremIO work.
zhaos2
643 Posts
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February 7th, 2014 19:00
Hi Sam, what the white paper are you reading, seems it it about Oracle best pactices for Oracle application with XtremIO? Will be appreciated if you can share to us., thanks!
blue_or_white
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February 11th, 2014 18:00
In your reply – “And, yes, the entire copy operation occurs in memory and uses back end pointers only.”
For this, my opinion is that, the entire copy operation (redo archiving operation) is not totally XIO memory/metadata operation. Because the ARCH process will first need to read from the online redo log, which would incur physical read IO from the array to the host; and the ARCH process would then write the the redo data from the host to the XIO array, which incurs memory/metadata operation and pointer update in the XIO array due to its dedup feature, no physical write IO incurred in this step.
Anonymous
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February 21st, 2014 02:00
I do agree with B_or_W, except if application use XtremIO snapshot mecanism (which is still to come) it will read data in order to copy it. in this case XtremIO will inline deduplicates IO writes. so the correct sentence would be someting like
"when you have to copy a closed redo log file to the archived destination, the operation duration is significally reduced. The operation remains a foreground-copy operation, therefore, the array does not perform actual physical I/Os Write to the back end; instead, it sends updates to in-memory pointers."