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How and whether to migrate from RAID 1 to RAID 5 on Dell Poweredge with PERC 4/Di

Posted on 2011-03-24
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We have a Dell Poweredge 2900 with PERC 4/Di  and with SBS 2003.  We are running out of space on the system partition. The current setup is system partition RAID 1 and the rest as RAID 5.  I am trying to find a way to expand the system partition without reinstalling and while on the phone to Dell about a new battery, they mentioned this as a possible way to do it.  I would like to ask what people's opinions are.  I was thinking it might be possible to add a couple of new hard drives, expand the RAID 5 array and then migrate the existing RAID 1 to RAID 5.

Thanks in advance
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Question by:beechfielder
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by:robincm
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by:PowerEdgeTech
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You can do what you are suggesting ... it is called a Reconfigure, and you can easily Reconfigure a RAID 1 to a 3 (or more)- disk RAID 5.

Once you have put the new drive(s) in , if you have OpenManage Server Administrator installed, go to Storage, PERC, Virtual Disks, and Reconfigure from the dropdown for the RAID 1.
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Be sure of your controller though ...

The PERC 4/Di is not used on a 2900, so you either have a PERC 5/i or PERC 6/i, or you have a SAS 5/iR or 6/iR.  The SAS 5/6 only support RAID 0 and 1, so reconfiguring is not an option.  But, if you have a PERC 5/6, you can easily do this.
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by:beechfielder
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Thanks

Ok, the perc 4/di must have been the previous 2300.  Do you know if I can get the version from the service tag?

Also, what are your feelings about performance?  this is a file server mainly but we do have a SQL database on it too

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by:beechfielder
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Thanks Robincm, the article mentions that only the last partition can be expanded, as it is the system partition it would mean deleting the other partitions, which I prefer not to do, unless I have misunderstood the article
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As far as extending the partition after expanding the RAID 1 to a RAID 5, you will need to extend it in one of two ways:

1. Third-party partitioning utility for servers (like Acronis Disk Director) that can move/resize partitions while keeping data intact, or

2. Use a free utility to extend the system partition, but as has been pointed out, nearly all free partitioning options to extend C: (Dell's ExtPart, GParted, 2008/Vista-family DVD, etc.) can only extend into Unpartitioned Space, which will require you to backup and delete those partitions before extending C:.

You will generally experience a hit in write-performance on a RAID 5, as parity needs to be calculated and written with the data.  If it is not a real active database, then it should be ok, but if it is pretty busy, then you might consider another alternative.

You can go here to for order details that should tell you:
http://support.dell.com/support/topics/global.aspx/support/my_systems_info/details?c=us&cs=04&l=en&s=bsd&servicetag=GSVNB71

Also, if you have OpenManage installed, you can get it there, under Storage.
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by:beechfielder
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Thanks the information is much appreciated. I have another question.  I had thought that if I reconfigured to RAID 5, I would be able to increase the disk space by adding more physical disks to the array and increase the system partition that way, rather than use a disk partition utility,  does what you are saying about extending the partition mean that this is not the case?  Also, another question that comes up now regards the space available,  If I reconfigure to RAID 5, I suppose I will lose space as it will need a third for parity info.  The partition is 50GB at the moment, with 20GB free.  

I dont mind the hit in performance, would rather take that than have to reinstall and redo the domain at the moment.
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by:beechfielder
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in Open Manage it shows Perc 5/i integrated
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by:beechfielder
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thank you for your help
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by:PowerEdgeTech
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Ok ... PERC 5/i, let's take a look at this scenario:

You have two 160GB drives in a RAID 1
You have three partitions: C:, D:, E:

RAID 1 is 160GB
Total disk space available to Windows: 160GB (minus a little for the disk-space math, but we'll ignore that for this scenario)
C: Partition: 12GB
D: Partition: 128GB
E: Partition: 20GB

If you Reconfigure your RAID 1 to RAID 5, then you will have a RAID 5 that is 320GB, but the Windows partitions stay the same size, so this is what you would have in Windows Disks Management after reconfiguring:

C: Partition: 12GB
D: Partition: 128GB
E: Partition: 20GB
Unpartitioned Space: 160GB

You will then need to find a way to utilize that 160GB of Unpartitioned Space to "grow" C:, by either deleting D: and E:, then extending C:, or using a third-party partitioning utility to do it while keeping other partitions intact.
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"I had thought that if I reconfigured to RAID 5, I would be able to increase the disk space by adding more physical disks to the array and increase the system partition that way, rather than use a disk partition utility,  does what you are saying about extending the partition mean that this is not the case?"

Just to answer your question directly:  Adding disks to the array will make more space available to Windows, but Windows cannot utilize that space until you've told it what to do with it.  

"Also, another question that comes up now regards the space available,  If I reconfigure to RAID 5, I suppose I will lose space as it will need a third for parity info.  The partition is 50GB at the moment, with 20GB free."

Remember, in both cases, RAID arrays and Windows partitions are not tied together ... Windows is oblivious to the fact that there is even more than one disk attached.  The RAID controller handles the array and individual disks, then tells Windows ... here is a "disk" you can work with, then Windows partitions it however the user requests or Windows requires.
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by:beechfielder
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Ok I am with you.  I just quake at the idea of moving the Exchange information store, which is on D, to extend the system partition.  I have a disk partitioning utility, by Acronis and have used the old powerquest partition app on clients, but never on a server.

Thank you very much for your help, I am a lot clearer now
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by:beechfielder
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Ok, one question, which might just contradict what I said about being with you.  Our data is on a RAID 5 array on two windows partitions, but the C partition is RAID 1, how does it mirror one partition, but use parity for the second
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by:beechfielder
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Final point,  there is no real reason to change from RAID 1 to RAID 5 then, I could just add some disks to the array and then repartition with a disk partitioning application as above
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by:PowerEdgeTech
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If your C: partition is the only partition on the RAID 1, then it will be fairly easy, as you won't have to worry about deleting any partitions:  After reconfiguring the RAID 1 to RAID 5, you will still have Unpartitioned Space at the end of that disk, but you can use Dell's ExtPart, a 2008/Vista/7 DVD, GParted or a host of other free partitioning utilities to extend C: into that Unpartitioned Space.  

The partitions do not use mirroring/parity ... all that is handled by your RAID controller on the individual disks.

The RAID 1 that your OS/C: drive is on has no parity ... it keeps two identical drives.  If you convert it to a RAID 5, then it will create a parity bit to be stored with the data across all 3 (or more) disks.
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"There is no real reason to change from RAID 1 to RAID 5 then, I could just add some disks to the array and then repartition with a disk partitioning application"

The only way to add space to your array is to add disks to it.  RAID 1 has only and exactly 2 disks, so in order to add disks to that array, it is necessary to "reconfigure" your RAID 1 to a RAID level that can have more than 2 disks ... RAID 5.
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Thank you again, I will go ahead and do it.  Also, I assume even without adding more disks the change from mirroring will free up some space, although a third will be taken with parity info.
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Without adding disks (keeping only 2), it will let you reconfigure your RAID 1 to a RAID 0, which will still double your available space, but I wouldn't do that.  RAID 1 keeps two identical disks, so if one fails, the other one contains all the data and keeps the server up and running.  With RAID 0, if you lose one disk, the server goes offline and your OS is gone.

If you are going to reconfigure to add more space, add a drive and reconfigure to RAID 5.
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