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how to add addtiional HDD to existing RAID 5 partition

Posted on 2014-04-17
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Hi
How can I add additional HDD (to expand) to existing RAID 5 partition .
I have one logical volume consist of  6 SAS HDD running on a IBM MegaRAID 10i in RAID 5.
I want to add two additional same size HDD and want to increase the volume space of one partition namely DATA.  I have two partitions, one is SYSTEM and the other is DATA. I just want to add the extra space to the DATA.
Thanks
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Question by:peteryau
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by:dlethe
ID: 40007096
The additional HDD expands the size of the physical volume, NOT the partition.  So what will happen is you will end up with additional free space at the end of the last partition.

Assume each disk is 1 TB, and SYSTEM is 1 TB, data is 4 TB.  So you have a 5TB total target drive.

Add 2 new drives, there will be 2TB unused. You then expand the partition using whatever O/S utilities are appropriate for your O/S.    If using Windows, you use disk administrator to resize DATA, assuming data is the 2nd partition, and free space is right next to it.

Note - best practice is to always do a full backup before resizing partition, and making sure all apps using DATA are shut down first.
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by:andyalder
ID: 40007408
Make sure that you do not go from less than 2TiB (2.2TB) to greater than 2TiB unless it was created as GPT disk, in most cases it would be a MBR disk if less than 2TB and if you grow that past 2TB you may not even see the current data any more.
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by:peteryau
ID: 40008143
I have already 6 x 300G HDD in RAID 5 config,  with 1 SYSTEM partition and 1 DATA partition.
How do I add the 2 extra 300G HDD (remain its RAID 5 config and keep the existing data) to just  the DATA partition. I just want to expand the DATA partition. Is it possible ?
In  my past experience in other server raid , I could only config the two extra HDD to the existing RAID 5 by create a new volume (e.g. DATA2).  I don't know if IBM MegaRAID controller could allow me to do what I want.
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by:dlethe
ID: 40008176
It does not work that way.  The logical volume that you partitioned will be 600GB larger.  THEN you expand the partition for the data and expand the filesystem.  

One action involves the RAID controller only, the other one is an O/S   + filesystem operation.

Use the Megaraid utility and look for option to expand the target device, or logical volume. Note some controllers and firmware may not let you do expansion unless you have a battery backup unit.
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by:peteryau
ID: 40008242
Hi diethe
I look into the diskmgmt of the server2008 and there is only 1 basic disk with two partitions - SYSTEM and DATA.
In the megaraid utility, I think I can modfiy the RAID drive group to have 2 more hard disk.
The point I don't know what to do is. After I expanding the drive group , what should I do on the  windows server to add the addtional space to the DATA volume?
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by:andyalder
ID: 40008442
LSI make it unnecessarily complicated but under the disk group properties you can select advanced options and add the physical disks there and then you can migrate logical drive to extend the drive that Windows sees. The free space is added to the end of the logical disk so as dlethe says you just extend D: using disk management or by using diskpart.exe. using iskpart to extend a data volume is described at http://support.microsoft.com/kb/325590/en-gb, do not convert it to dynamic.

Fortunately you are not going to cross the 2TiB barrier, be aware that you will not be able to add a 3rd disk in the future this easily.
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dlethe earned 500 total points
ID: 40008503
P.S. It is always best practice to do full backup before beginning this procedure.  Extending the RAID is quite I/O intensive and touches every physical block on all drives, so is I/O intensive.  If disks are  old, and/or you don't have a UPS with battery backup, then beware of Murphy's laws.

I  have seen people get 100% data loss in multiple failure scenarios on rebuilds with RAID5.  Personally, I would just add 300GB and convert to a RAID6 if the firmware lets you -- which it should.

RAID6 doubles the data protection, and unless you are write intensive, it won't have any significant performance hit, but will let you sleep at night if you lose one HDD, because you will still be protected against a drive failure or a bad block.

Remember RAID5 does NOT protect against data loss if a disk dies.  It ONLY protects against data loss if a disk dies AND 100% of the trillions of other blocks you have are readable.
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