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Hot swap mirror drive in Windows 2008

Posted on 2009-05-05
Medium Priority
Last Modified: 2012-05-06
I'm implementing a new backup strategy for my server.  The server is a Dell Poweredge 1950 with 2 Hot Swappable SAS drives. One drive is 300 GB and the other is 500 GB. The OS is installed on the 300 GB drive.

For one of the layers I was planning to set up a mirror drive per the instructions found here: http://support.microsoft.com/default.aspx/kb/951985.  My thinking is that I'll set up a mirror (or shadow) partition on the 500 GB drive and use the rest of the space for application specific backups (i.e. sharepoint, exchange). I'll then take the drive out and put it in a safe when I leave for the evenings.

My question is basically, is there any reason that my little plan wouldn't work? I'm new to mirroring drives, so I'd appreciate any advice.

Question by:steam23
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Expert Comment

ID: 24305932
Mirrored drive are best practice for failover, not backup.
The hot swap is for security, not every day use...

Also, you'll configure a hardware raid (as opposed to windows software raid), and I don't think the remaining space will be available.

My advice: get a proper external drive (tape or HDD) for your backup, and leave your raid in peace.
LVL 35

Expert Comment

ID: 24306515
Yeah, I would follow maze-uk. Hot-Swap drives are intented for RAID failovers. Most of the backplanes are not intended to unplugg an plug again drives on a daily base. You will destroy the backplane earlier or later.

Also a mirror is not intended to run all the time in degraded mode. Every change of a drive will initialize a full sync of the drives, which can take several hours and slows down everything.

If you want to realize a cheap backup solution, you may think about some USB hard drives, you can use for backups (not for mirroring).  

Author Comment

ID: 24306654
So basically, you guys are saying that the only point of setting up a mirror is to protect against the drive failing. Since the drives are the same age and mirrored, therefore completing the same number of transactions, wouldn't they be more llikely to fail at the same time? If so, what would be the advantage of doing a mirror in the first place?
I have a USB drive that I'll be using for backups, my original plan was to make that a weekly backup that i keep at home. That was why I was thinking of using the hot swap drive for daily backups. Maybe instead I should not set up a raid and take the hot swap drive home instead. That way I'd only be plugging it in once a week. Would I still be killing my backplane if I was just plugging the drive in once a week?
LVL 35

Accepted Solution

Bembi earned 2000 total points
ID: 24307012
> So basically...
Mirrors should protect a system from drive failures. In case of a damage, the system can stay online which the remaining disk. If the failing drive is replaced, the systems makes an automatic resync of the drives. Otherwise the system would crash.

This method is mainly used for servers or very important workstations to get them up and run, also in case of a drive crash.

Usually, if two drives are crashing at the same time, you should play some lottery, the probability of that case is low (but not impossible). For higher security needs, a RAID 5 (or higher) system maybe recommended, as they may provide a higher fault tolerance (dependend on the Raid Level).  

But the intension was (and is) never a file backup. What some admins are doing is to build up an initial mirror and then they replace one of the drives for the ultimate worst case szenario.  New mirrors are then taken when essential configuration changes are made. In this case, you have 2 drives within the online mirror and a third drive to boot up the system in case of a fatal error.

A common way to protect servers is to build up a mirror for the system drive an a Raid 5 for a second data drive to seperate static data from dynamic (often changing) data. Also, in case of a fatal crash, you will loose only one part, either the OS or the data. this allows a faster recovery of a system. As a OS can be reinstalled from the original sources, the security needs of the OS is lesser than for data.

The backplanes are developed for the case of a drive failure. This may happen in normal cases once in two or three years. Every change of a drive will stress the contacts and they will get more and more worse. One day, you will experience sporadic drive failures or other issues due to bad contacts, which are running out of the tolerance. At this point, you should better throw away the complete backplane.

From my point of perspective, let the mirror run as it is. Avoid changing the drives if not needed. Seperate the source system from a backup system and do not use components from the source system for the Backup. A seperate system like a tape device or USB drives are completely independend from the source system and maybe recoverable on diferent hardware. If your backplane fails, there is no fast recovery option anymore and you can never be sure, that no data is damaged.

Take two or more USB drives, make a weekly full backup (alternating with two drives, so you can always keep one drive at home) and daily incremental backups, and whatever will crash, you can restore the last state. The system is the same like with tapes. For this, you can take cheap SATA drives. Nevertheless, a tape system is always the more robust system, as it is easier to destroy a drive than a tape.


Author Closing Comment

ID: 31578066
Great post! Thanks for taking the time to clear that up!

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