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Sybase disk mirror

motioneye
motioneye asked
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Last Modified: 2012-05-07
I have configure the disk mirror on my Sybase machine, How do I monitor the progress of mirror? how will I notice my mirror going down or issue occured ?
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Maybe you are coming from the MicroShaft world, and you need to check that things are working all the time.  In the Sybase world, things do not break, and if they do break (for reasons beyond ASE control, such as a disk going down) you will get error messages.  These are logged in the errorlog file, which is located in:
C:\sybase\ASE-12_5\install
with the RUN_SERVER files.  You should be inspecting the errorlog regularly.  On Windoze, you can set it up to log messages in the system event log as well.  Most of us have either the errorlog piped to a window on our DBA desktop, or a simple shell script running that scans the errorlog and sends us email if an error is logged.

The deterministic question is:
Do you monitor normal disks, ie. unmirrored disks, or all your disks before you initialised your mirror ?
You need to do the exact same monitoring for the mirrors.  Nothing less, nothing more.

If a disk device (a mirror is just another disk device) goes down, an error will be logged.  If the disk is mirrored, there is no effect on the users, the mirror will keep going, and you can re-create the new disk somewhere else.  If the disk is unmirrored, all writes to the failed disk will fail, and users will be affected.

I am not sure what you mean by "progress" of the mirror.  The mirror is active 100% of the time, all writes to the device will be duplicated to the mirror device.  It is only when you start a new mirror that there is an initial witing to it, to make it a mirror, a "catch-up" period.

For monitoring the activity on both the device and the mirror device, use sp_sysmon.  Or any one of the available good 3rd party monitoring tools.

I am not saying that you should not use Sybase mirroring, but you should evaluate doing the mirroring at the Disk Controller or Volume Manager level.  This is much faster, because it is middleware, and it releases ASE from the task, which allows those free cycles to be used for the other things ASE does.  Sybase mirroring was essential in the old days, before Volume Managers were available, but since their advent, it is the slower choice.  Additionally, with a VM, you can configure and re-configure the entire disk array for the server (or several servers), not just the Sybase devices.  Sybase mirrors remain essential and are excellent for other purposes (not relevant to this question).

Author

Commented:
Hi,'
Thanks for this very long explicit explanation, Yes I'm 100% belongs to Mcsft, It was 10 years back my day with Oracle RDB running on VMS and since then I'm dedicated my self with Mssql + windows :(.
well what I'm trying to say with "progress" is just need to know if this sybase mirror provide us with any command or sp which we can monitor how mirror works at least we know on what command being mirrored to mirror device, if u said we can 100% trust on sybase mirror, then I have niothing much to say :)

< If the disk is unmirrored, all writes to the failed disk will fail, and users will be affected.> is this means we have to immediately to remirror to avoid from downtime ?
do you know when should I activate the mirror device? is that only upon primary device failed/corrupted  is that anyway which mirror will take over immediately upon primary crashed?
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Author

Commented:
very gud explanation indeed
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