alaaalii
1 Copper

Expand RAID 5 array with extra disks

Hello. I have a Dell PowerEdge R720 server. It currently has 12 900GB drives. The server is running Red Hat Linux.

  • 2 drives configured with RAID 0 or RAID 1, can't remember. Virtual Disk 0.
  • 10 drives configured with RAID 5. Virtual Disk 1.

Virtual Disk 1 only has one partition, /dev/sdb1. I want to increase the size of this disk. I want to add 3 more 900GB disks to the RAID 5 array. What are the steps to do this? I can access the iDRAC interface of the server to manage it. Here is what I've got so far:

  1. Add the physical disks to empty slots on the server.
  2. Access the iDRAC interface (or maybe the Ctrl+R utility when booting?) and add the extra 3 disks into the array. I'm not sure if I need to "delete" the array, or do I just "add" the slots to the array?
  3. "Reconfigure" the array. After this step, I think the drive will now have the extra space.
  4. In the OS, expand the partition to use the extra unallocated/free space. I know the steps for this part.

I do not want to lose any data on the RAID 5 array, and I want to avoid rebooting (I guess I could reboot if push comes to shove). My concern is with steps 2 and 3. Does "reconfiguring" the array delete the data? Also, do I need to unmount the (only) partition on the drive to add the disks to the array? Or is it done "live" or "online". Also, how much disk space will these 3 extra 900GB drives add to the array? Is there a simple calculation I can use to figure out how many disks I need to add X number of TBs, given the disks will always be 900GB?

I don't have access to the server right now, so I can't give more information on the RAID controller name and version. But just an FYI: we once replaced a failed drive by swapping it out with a new one without having to shut down the server. Maybe this bit of info can shed some light on the RAID controller.

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theflash1932
6 Indium

RE: Expand RAID 5 array with extra disks

Access the iDRAC interface (or maybe the Ctrl+R utility when booting?) and add the extra 3 disks into the array. I'm not sure if I need to "delete" the array, or do I just "add" the slots to the array?

I do not want to lose any data on the RAID 5 array

First, I'd suggest NOT deleting your VD if you don't want to lose data. 

You can do this without data loss, while the array is online, and without rebooting the server, but you need to use OpenManage Server Administrator to do it.  Here is the download for RHEL 6:

http://www.dell.com/support/home/us/en/04/Drivers/DriversDetails?driverId=T9GYK&fileId=3365593027&os...

I don't have experience installing it in Linux from which to give you any steps or advice, but once it is installed, you will find "reconfigure" under Storage, Virtual Disks, dropdown menu for RAID 5.  This will happen while the RAID 5 is live, online, and even in use (although with degraded performance).  Once it is complete, you will need to manage the partition yourself (extending current partition), as it won't be automatic.  The "disk" will now be bigger, but the partitions will remain the same size until you extend them.

Is there a simple calculation I can use to figure out how many disks I need to add X number of TBs, given the disks will always be 900GB?

You will get roughly 93% of the advertised drive space (837GB for a 900GB drive), and RAID 5 always uses one-disk's worth of space for parity across the array, so once it is configured, each disk you add will add that much to the overall storage.  So, adding 3x900GB drives will increase it about 2.51TB.  On that note, 10TB is a pretty good size array ... I would recommend you further protect it by converting it to a RAID 6, which will give you two disks' worth of parity.

I don't have access to the server right now, so I can't give more information on the RAID controller name and version. But just an FYI: we once replaced a failed drive by swapping it out with a new one without having to shut down the server. Maybe this bit of info can shed some light on the RAID controller.

No, that is a feature of all systems with hot-swappable drives.  It is possible you have an H310, but it is far more likely you have an H710.  If you have an H310, I'd recommend you upgrade to the H710 for this setup.

 

Moderator
Moderator

RE: Expand RAID 5 array with extra disks

Alaaalii,

To expand the raid 5 without downtime you would need to install OpenManage Server Administrator (OMSA) on the server and then perform a Reconfigure under the raid controller in OMSA. If you can down the server you can also do a Reconfigure in the raid controller under Virtual Disk Mgmt as well. 

Before resizing a partition, boot into rescue mode (or unmount any partitions on the device and turn off any swap space on the device).
Start Parted, where /dev/sda is the device on which to resize the partition: For example -
parted /dev/sda
View the current partition table to determine the minor number of the partition to resize as well as the start and end points for the partition:
print
To resize the partition, use the resize command followed by the minor number for the partition, the starting place in megabytes, and the end place in megabytes. For example:
resize 3 1024 2048

So long as you do a resize and don't replace it the data should remain intact.

Let me know if this answers your questions

Chris Hawk

Dell | Social Outreach Services - Enterprise
Get Support on Twitter @DellCaresPro 
Download the Dell Quick Resource Locator app today to access PowerEdge support content on your mobile device! (iOS, Android, Windows)

alaaalii
1 Copper

RE: Expand RAID 5 array with extra disks

@theflash: this is all great, but some cases running the same application that's running on the server reported that installing OMSA caused significant performance issues and crashed the web server (tomcat) of the application. I just took a look at the OMSA interface from online articles and videos, and it looks pretty similar to the interface we get from accessing the dedicated iDRAC interface. Can I not do the same RAID configurations through iDRAC?

@Chris: that's only resizing the partition, but I'll have to still resize the filesystem using resize2fs right? I'm not used to using parted. I was going to delete the partition using fdisk and recreate it to take up the extra space, then use resize2fs to resize the filesystem to use that space.

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Moderator
Moderator

RE: Expand RAID 5 array with extra disks

Alaaalii,

In regards to expanding the array this is the only option. You can't expand the array in the Drac or even in the raid BIOS itself. OpenManage is the only way to extend an existing array.

In regards to the partition. The OMSA expansion is for the array, the commands I shared with you would be to resize the partition that is within that array.

I hope this helps 

Chris Hawk

Dell | Social Outreach Services - Enterprise
Get Support on Twitter @DellCaresPro 
Download the Dell Quick Resource Locator app today to access PowerEdge support content on your mobile device! (iOS, Android, Windows)

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lazzio
1 Copper

RE: Expand RAID 5 array with extra disks

Hi Chris,

i need your help here :-)

this is my situation:

customer ordered wrong HDDs  with size 600GB, but app needs 1,2T  now.

i have installed open manage sw but i have screwed up data , because before resizing i did not umount partition.

so when raid will be reconfigure in omsa , then i will umount affected partition  and then i will run parted,,

but ,on the system is parted version 2.1 and it has problem with resizing ext4 FS.

i have found and successful testing following :

Run parted on your device: parted /dev/sdX
Change display unit to sectors: unit s
Print current partition table and note the start sector for your partition: p
Delete your partition (won't delete the data or filesystem): rm <number>
Recreate the partition with the starting sector from above: mkpart primary <start> <end>
Exit parted: quit
Check the filesystem: sudo e2fsck -f /dev/sdXX
Resize filesystem: sudo resize2fs /dev/sdXX

do you think its gonna be without problem on physical machines as well ?

Thank You

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