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Go to SolutionWhat happens with the data during a meta expansion using BCVs
I expanded metas several times now and it works great. During the symconfigure I tried watching the BCVs syncing back and forth, but I guess this is not exactly how the data flow goes.
Can anyone explain to me what happens to the data during the expansion ?
I'm using the folllowing syntax:
add dev 2D4C:2D51 to meta 16D0, protect_data=TRUE, bcv_meta_head=1655;
Furthermore I found out that you need 2-way-mir-BCVs for this, not RAID5 BCVs (Clones). Since I ran out of my RAID1 storage for use in the latest expansion, I was forced to use a few 500GB7k2 spindels, which weren't used yet instead of the 73GB15k spindels and I must say I didn't even notice a significant difference in the BCV establish and syncing process.
Can anyone explain to me what happens to the data during the expansion ?
I'm using the folllowing syntax:
add dev 2D4C:2D51 to meta 16D0, protect_data=TRUE, bcv_meta_head=1655;
Furthermore I found out that you need 2-way-mir-BCVs for this, not RAID5 BCVs (Clones). Since I ran out of my RAID1 storage for use in the latest expansion, I was forced to use a few 500GB7k2 spindels, which weren't used yet instead of the 73GB15k spindels and I must say I didn't even notice a significant difference in the BCV establish and syncing process.
570
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Posted November 12th, 2007 06:00
The process of data being copied from the meta to the BCV is something I can follow (run a symmir query command and watch the SyncInProg run), but the restore somehow is invisible (or simply not done using a "BCV restore").
I suspected the copy back from BCV to meta only to be needed when something goes wrong, because I couldn't see the copying back to the expanded meta taking place. So if I understand correctly, the BCV really is used and not just there for backup purposes ?232
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Posted November 12th, 2007 06:00
This is to be expected, there is an entry created in the GDAT table for the relationship that gets created between the original BCV and the STD, once the BCV is established to another device this will be cleared.570
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Posted November 12th, 2007 06:00
Paul,
the BCV that is used for protecting data, it needs to be the size of the meta being expanded, or the future capacity of the meta being expanded ?
Thanks516
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Posted November 12th, 2007 06:00
You are correct, the BCV will actually assume a
mirror position on the STD, thus protecting you from
any data unavailable situation during the meta
expansion.
once the meta is expanded the BCV is released ?232
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Posted November 12th, 2007 06:00
No, the RAID level doesn't need to be identical.
So a 200GB RAID5 meta can be expanded using a 200GB 2-way-mir BCV. In fact: this is how we do it. We don't have RAID1 for production (I know, it's silly, but our customers are served by RAID5 only atm).570
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Posted November 12th, 2007 06:00
Simply expand the BCV then with the same number of ldevs as you expanded the original meta with ?
I have a pool of RAID1 storage just sitting there to be used for use in expansion changes. I configure it on a per case scenario with number of meta members and perhaps cylinder sizes etc etc286
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Posted November 12th, 2007 06:00
Yup. But if anyone asks for a meta expansion of more than a TB, I think we're running into probs after all. Growing from 200 to 300 is ok, but the larger they get, the more temporary BCV space I need570
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Posted November 12th, 2007 06:00
you're well covered then570
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Posted November 12th, 2007 06:00
The BCV being used for the expansion should match the original STD Meta, i.e. have the same meta count/number of cylinders etc. It is not available for future incremental establishes with the newly expanded meta.
rawstorage
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570
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Posted November 12th, 2007 06:00