LVM mirroring

[K.C. Chan]

All,
I plan to mirror my oracle filesystem. But I am not certain on a few options. Can option -M y and -c y (Mirror write cache and Mirror consistency) be used together (are they mutually exclusive?). Thanks.

[James R. Ferguson]

Hi:

No, the man pages for 'lvcreate' answer this.

'-c mirror_consistency' is effective only when '-M n' is specified. It is ignored for '-M y'.

Regards!

...JRF...

[Steven E. Protter]

Small tutorial:

Since the filesystem is already created, lvcreate is not the command to even discuss.

The prior post covers it anyway.

All that covers is how the mirror is recovered if it gets out of synch.

Process:

lvcreate the logcial volume
lvcreate -C y -n oracledata /dev/vg01

# Creates a contiguous required volume named oracledata in volume group vg01

lvextend -L /dev/vg01/oracledata /dev/dsk/c#t#d0

replaced the # signs with real disk

lvextend -m 1 /dev/vg01/oracledata /dev/dsk/c#t#d0

make the disk obviously a second valid disk.

Done, you are mirrored. If one disk fails, the database chugs on.

SEP

[K.C. Chan]

fyi, sorry for the confusion, no filesystem or lvol has been created yet. I am concerned about the two options.

Since they are mutually exclusive, then I wonder what would be best. Mirror write cache or Mirror conistency? Could someone share their experience on this issue? Thanks.

[James R. Ferguson]

Hi (again):

If the logical volume has already been created, your options are defined in the man pages for 'lvchange'.

At 'lvcreate', the mirror write cache is *on* by default ('-M y') as is the mirror consistency flag ('-c y'). As the man pages for 'lvcreate' specify, setting mirror consistency *on* is actually *ignored* when the mirror write cache is enabled.

A good guide to how these choices interpolate can be found in the Technical Knowledge Base document #KBAN00000180.

Regards!

...JRF...

[James R. Ferguson]

Steven:

You wrote, "Small tutorial: Since the filesystem is already created, lvcreate is not the command to even discuss."

Please note that that was not explicitly stated by the author. Further, the author specifically asked about using the mirror_write_cache and mirror_consistency options.

You did not address the later. Please reread my first post before you say "Small tutorial...lvcreate is not the command to even discuss".

...JRF...

[K.C. Chan]

All,
I just want to know if mirror write cache and mirror write consistency is mutually exclusive or not. Now that I know, my next question is which option of the two is best for an oracle database? If you need more info, such as type of raid or hardware, please let me know. Thanks.