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Currently I have 8 disks each of size 32G forming a RAID 10. Now, I want to increase the size of this RAID by adding extra disks. This is a production device so there is already critical data in the RAID. The filesystem is XFS. Is there any way to increase the size of this RAID without affecting the running read/writes on that RAID. If not, how to do this with minimum offline time ?

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Are you using hardware RAID or software RAID? – ewwhite May 18 '13 at 12:47
@ewwhite: software RAID. – pradeepchhetri May 18 '13 at 12:48

There are 2 cases:

  1. you add new drives The easiest and safest way is to create a new array on the new drives , create a physical volume on the new array and here you are. No loss of performance here. As a bonus you can create a new volume group in order to put your data in one array or the other.
  2. You replace existing drives with bigger ones Replace them one by one, each time create 2 partitions on the disk. You add the first (for example sdX1 to the existing array ( it should recover automatically ) and you can then create a new array on all the second partions ( the sdX2 ). Depending on your usage there might be a performance hit for some operations ( basically if you copy data between both arrays ).

In both cases you won't lose data and if your hardware allows hotplug you will not have downtime.

By the way even if mdadm allowed a dynamic resize of the array I would not take the chance with production data.

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Can the second method be used for increasing RAID 10 created using mdadm ? – pradeepchhetri May 18 '13 at 13:36
in the second method you will have the existing array + a new array – Olivier S May 18 '13 at 13:59

Assuming this is on Linux with mdadm - you can't.

mdadm does not support growing RAID10

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you mean i need to create a new raid and copy the whole data. there is no other way ? – pradeepchhetri May 18 '13 at 12:47
Yes - you can't grow a RAID10 array with mdadm. If you anticipate growing the array and performance isn't too critical - use RAID5 or RAID6 – choco-loo May 18 '13 at 12:48

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