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Backup with RAID and Hot-swappable drive

Posted on 2005-04-05
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I have a hot-swappable SATA bay installed in Windows 2003 Server machine.
I am trying to figure out the best way to create a mirror system, where I could hot swap one drive for backup purposes.
One should be able to walk into server closet, slide out drive from bay (completely mirrored to have all data on it), slide in new drive and walk away.
(my father is needing this for his business, but has to be extremely simple for him)

I have four identical SATA 200G drives, a Vantec SATA hot-swap bay with extra cartridge, and a 3ware SATA RAID controller (4 port).

All thoughts are appreciated.



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Question by:txcde
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10 Comments
 
LVL 3

Expert Comment

by:kdkirmse
ID: 13709524
I dont think the process will be as simple as you would like. When I have worked with 3ware controllers there has not been an option to automaticly start rebuilding a mirror when a new drive in inserted into a hot swap bay. You have to use the 3ware control software to initiate this process.  
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Author Comment

by:txcde
ID: 13709623
I am open for purchasing any controller that would simplify the process.  
Also, SoftRAID (for Mac only it seems) offers a software-based solution similar to what I am trying to achieve.

Is there a way to automatically rebuild a mirror in the background while OS is running?
The problem lies with the server being down for two hours while rebuilding in a controller BIOS state.

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LVL 3

Expert Comment

by:kdkirmse
ID: 13710115
The mirror will be rebuilt in the background using any modern controller including a 3ware. In the case of the 3ware controller the management is done using a local web page on the server. The server does not have to be brought down to do this.

The process could be.

1) remove mirror drive.
2) insert new drive
3) run raid control software to replace the removed old drive with the new one.
    mirror recovery will start.
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LVL 12

Expert Comment

by:Carlo-Giuliani
ID: 13711294
Many RAID contollers (in fact, every one I have every worked with) will rebuild a mirror without interrupting normal operation (although performance will suffer).    You *can* do the rebuild using the BIOS-based utilities, but you don't need to do it that way.   If you restart the server with a redundant drive missing, it will probably prompt you to do something during the boot-up....you may be able to configure it to go ahead without such a prompt.

However, reading the posts so far I am worried that you seem to think you can pull out a backup copy while the system is running.  That is *not* safe.  You don't have to shut down the server to rebuild the mirror, but you *should* shut down the server to take out a backup copy.  Just removing a drive while the server is running is like flipping the power switch while it is running (from the point of view of the drive you removed).

To make a new backup (assuming mirror is in place)
=================================
- Shutdown the server
- Remove one mirrored driver (it should not matter which)
- Restart the server (running with a mirror drive missing)
  You may have to reply to a boot prompt to confirm startup with a missing drive.
- Insert a new drive -- rebuild should start automatically -- controller software may allow you to monitor it.

Server performance will be reduced during the rebuild.
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LVL 3

Expert Comment

by:kdkirmse
ID: 13711491
The drive carriers are listed as being hot swap capable. As such they are designed to have the drive be removed and inserted while a system is running. This is a capability that is standard in fibre channel and certain SCSI drives. SATA drives also have this capability but most motherboard controllers do not support the process of hot swap. The problem with hot swap is rarely drive removal but in insertion. Devices that support hot insertion have specially designed connectors with pins of different length as to stage the powerup and powerdown of the component in question.

Here is a paper from maxtor describing the SATA hot swap capabilities:

http://www.maxtor.com/_files/maxtor/en_us/documentation/white_papers_technical/sata_hot_plug_white_paper.pdf
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LVL 12

Expert Comment

by:Carlo-Giuliani
ID: 13711716

Removing a drive may be perfectly safe from the point of view of the drive, controller, and motherboard, but it also has to be OK with the operating system and application software.  You don't want to remove the drive while the application is in the middle of writing some updates to it. If there are nosystem files on the drive, and you can dismount it in the operating system, then you can remove a  clean mirror copy while the server is still running.  But what's the point, if you had to stop the application to do this??  

If the goal is simply to get a complete system and/or data copy with miminum downtime, the simplest and safest procedure is to shutdown the server.    You can the restart without waiting for the mirror be rebuilt, and so keep the interruption of service to a minimum.
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LVL 27

Expert Comment

by:Exchange_Admin
ID: 13712454
Ok I may get flamed here but this is my opinion:
You should never ONLY rely on a mirrored set for backups. That is not the purpose of the mirror set. You should still perform regular backups.
How many times have people relied on a mirror set only to find out there was problems.

Better safe than sorry if your dad's company data is important.

Just my 2 cents worth.
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Author Comment

by:txcde
ID: 13718319
I currently utilize an online backup company for about 200MB of critial data, daily.

My main concern is the other 50G or so of software, pictures and other valuables that are too big to cross the inet, even with T1.
(not to mention 50G worth of storage is not cheap)

Here is what I have done (seems to work):

1)  Created RAID 1 with two identical 200G drives VIA the 3ware controller card.
2)  In W2003 Server, my 200G hot-swappable drive is set to be a mirror of the RAID 1 data drive


In order to pull the hot swap backup, I have to shut the PC down, swap drives, then boot up.  This sounds like a lot of trouble, but actually the software mirror solves the problem of long periods of down time while the BIOS RAID controller rebuilds a mirror.  W2003 Server merely synchronizes the data in the background upon boot-up.  Thus, my network employees hardly notice at all when drive has to be swapped.
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LVL 25

Accepted Solution

by:
kode99 earned 1000 total points
ID: 13720936
Hot swap backup with a mirror sounds great in theory but is not so good in practice.  There are two major issues here.

First, messing with the RAID array is going to cause performance hits,  if something gets messed up during a drive swap you could have issues with the array being messed up.  Depending on the interface to rebuild somebody could accidently remirror the wrong way etc.  

Second, possibly more important, is that during the rebuild process the RAID array is not providing any protection.  So if the master drive failed during a rebuild you are toast.  Depending on the controller and size of partitions the rebuild window can be fairly long.  If doing this regularly the risk is even larger.

I think you would be farther ahead to install two drives in RAID 1 then use the other two drives as swap out drive for backup.  So the data is backed up to a local non raid drive then pull the drive when it is done and put in the other drive.  This way you have a copy that is not 'live' and not subjected to the risk of failure of the system from some sort of severe power issue etc.  Much like a tape or other external backup.

Also the drive is not a RAID mirror but a plain volume so you can plug it into any machine and access the data with any system with SATA ports.

If you need a full backup I would go with something like Acronis True Image and have it write the backup images to the swap drive.  Then you could do a bare metal restore with the backup drive.  Since you would need a server version this will cost a few bucks but it is easy to use.
 
  http://www.acronis.com/

If you are only looking at backing up data then something simple like robocopy can be set up to do scheduled backups of files to the drive.  Its free.

  http://www.ss64.com/nt/robocopy.html

There are also some nice simple 'semi-live' backup programs that are very reasonably priced,  here are a couple

Backup on Demand
  http://www.caddais.com/BackupOnDemand.shtml

Second Copy
  http://www.centered.com/

These can also be set up to also backup revisions of files which can be very very handy.

I also fully agree with Exchange_Admin. Hard drives are fairly easy to damage.  Just dropping one during a swap procedure could render it useless.  Tapes are a more robust.  
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Author Comment

by:txcde
ID: 13727469
Great work!  A big thanks goes to all of you who replied to this thread.

This is a terrific site, and home to many outstanding computer admins.
Money well spent, here.


-txcde
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