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Software Mirror a Database

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Mad_1
Regular Advisor

Software Mirror a Database

I am using D-Class servers (HP-UX 10.20) currently, data store in Sybase with RAID 5 (Model 20).

The server will be upgrade to A or L class, my HP sales recommend to use sc10 as data storage with software mirror (MirrorUX). They said the CPU can perform mirroring efficiently.

Since sc10 can be hot swapped, if one of the mirrored disk is down, the database service should not be interrupted, the replaced disk can be synchronized.

But my concern is, is it need to stop the database during data synchronization, or need to restart the database after data synchronization?

Please help, thanks
10 REPLIES
Justo Exposito
Esteemed Contributor

Re: Software Mirror a Database

Hi Ryan,

If you have mirrorUx software, the sinconization process impact in the througput, but you don't need to stop your database. This is a O.S process.

Regards,

Justo.
Help is a Beatiful word
Vincent Farrugia
Honored Contributor

Re: Software Mirror a Database

Hello,

You can continue to run normally while a syncronisation is made. Of course, you will have a performance drop during this time, though.

HTH,
Vince
Tape Drives RULE!!!
Wim Rombauts
Honored Contributor

Re: Software Mirror a Database

Mirroring is fine and you can continue to work when a disk fails, but remember, when you use mirroring, you will need almost double as much disks as you should need in a RAID5 configuration.

Mirroring offers a higher degree of protection (multiple disks can go down, in RAID5 only one can go down and then you are unprotected). You can configure a hot spare to automatically take over the defective disk. But you will need more disks and there *IS* a CPU overhead. If a mirroring configuration with a "cheaper" disk box is less expensive than a configuration with a hardware RAID5 disk box, I think mirroring is a good choice.
harry d brown jr
Honored Contributor

Re: Software Mirror a Database

Ryan,

If you want better performance for your data, I suggest adding an fc60 in front of the sc10, and I actually suggest an fc10 over an sc10. If you are going to an L then get fibre channel cards.

live free or die
harry
Live Free or Die
Mad_1
Regular Advisor

Re: Software Mirror a Database

Thanks a lot for all your reply.


All I worry about is one of my colleague mentioned that in AIX, a database (raw device) need to restart after a software mirrored disk is replaced and need data synchronization. I afraid it will also happen in HP-UX.

It is my first time to post message here, I found it is very helpful, thanks all again.
Justo Exposito
Esteemed Contributor

Re: Software Mirror a Database

Hi Again,

This is because your collegue is using a raw device and then the device is not under the O.S. In your case if you have the database files under the HP/UX file system and with mirror/ux you don't have this problem.

Best Regards,

Justo.

PD: It's your first time, then don't forget to put your points to the replays.
Help is a Beatiful word
Darrell Allen
Honored Contributor

Re: Software Mirror a Database

Hi Ryan,

Yes, once you replace a disk the logical volume mirrors for that disk will need to be re-synchronized. However, there are commands that allow you to do this with the system up and running. Technical Knowledge Base document# KBAN00000347 gives instructions. I've attached it for your convenience.

My memory about AIX is fuzzy but I'm fairly certain you can mirror or re-sync logical volumes in AIX without stopping the app using those LVs.

Darrell
"What, Me Worry?" - Alfred E. Neuman (Mad Magazine)
Mad_1
Regular Advisor

Re: Software Mirror a Database

Actually, I am using raw device too in HP-UX, the Sybase database is storing in a raw device, so I am worry about "Does software mirroring can handle this - not interrupt a Sybase database (raw device)?"

As far as I understand, the MirrorUX (software mirroring) mirror the data in system level, all it knows is VG or LV, it doesn't care about whether it is a raw device or a file system, therefore, it sync the data block by block when one of the mirrored disk was replaced. Is it correct?
Roger Baptiste
Honored Contributor
Solution

Re: Software Mirror a Database

<>

Yes, you are correct. As long as you have the mirroring setup correctly for all the VGs on the system, it should work fine . When a disk fails, the database will still run since it has two copies (primary and mirror disk).
When a new mirror disk is attached, it will get synchronised automatically in the background. You don't need to bring the database down. But, during the synchronisation, there will be some performance bottlneck.

HTH
raj
Take it easy.
Tim D Fulford
Honored Contributor

Re: Software Mirror a Database

Ryan

It seems to me that you are familar with LVM terms but not the detail. There is one "GOT YA" (which does NOT effect your service/availability). You cannot simply swap out a duff disk for a new one and expect LVM to sort it out. You need to to a
# vgcfgrestore -n
to restore all the LVM headder & footrt info onto the disk. Then MirrorUX kicks in & does the rest. If you do just swap the disk it will just sit there unused & UNMIRRORED!

Also, you need to monitor LVM to check if a disk has broken. Things like STM, ITO etc can do this but one way to check if your disk is duff is to do
# pvdisplay /dev/dsk/ | grep -i stale
If you continously have stale extents the disk may be duff! (a stale extent is one that has not synced with the mirror)

All the above said disks rarely go wrong, I've NEVER used vgcfgrestore only only occasionally seen stale extents.

Tim
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