| RE: What does EXTERN, NORMAL, HIGH mean for ASM diskgroups? [message #63614] |
Wed, 20 October 2004 12:40  |
JOHN
Messages: 182
Registered: April 1998
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Senior Member |
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Hi:
We are not sure about what EXTERN, NORMAL, and HIGH
mean for ASM Diskgroup types.
For example, we have set up an ASM diskgroup with type HIGH.
Our understanding is that HIGH means there are three copies
of any file (i.e., two mirrors).
But, when Oracle starts writing out archvied redo logs to ASM,
why is there only one archived redo log written out?
Should there not be multiple copies?
If there is mirroring, where are the mirrored copies?
Also, could someone please post the official definitions of EXTERN, NORMAL, and HIGH for ASM diskgroups?
Lastly, we have a question about FREE_MB field in V$ASM_DISKGROUP.
If we are using HIGH type ASM diskgroup,
does the FREE_MB mean the real capacity avaiable to Oracle?
For example, if FREE_MB = 1 GB,
does that mean Oracle can write a 1 GB file to ASM?
If yes, are there any copies of new file and where do they go?
Thanks
John
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| Re: RE: What does EXTERN, NORMAL, HIGH mean for ASM diskgroups? [message #117875 is a reply to message #63614] |
Sat, 30 April 2005 09:39  |
Frank Naude
Messages: 4587
Registered: April 1998
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Senior Member |
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Hi,
External Redundancy = No mirroring (handy if you use hardware mirroring)
Normal Redundancy = 2-way mirroring (must have at least 2 failure groups)
High Redundancy = 3-way mirroring (must have at least 3 failure groups)
File extents are mirrored, however, you will only see one file (as would be the case with normal disk mirroring).
V$ASM_DISKGROUP.FREE_MB refers to usable free space within the disk group. So, if you have 1 Gig left, and you use high redundancy, you cannot fit-in a file bigger than 341MB.
Best regards.
Frank
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