RAID0 on lefthand P4500G2 14.4

[bublik]

 lefthand P4500G2 14.4

if I would create a volume with RAID0 I realize that there is no protection. But if single disk fails, would my entire volume be unavailable or in degraded state until I replace that disk?

[Rukam]

Hi

In RAID 0, always power off the drive in the CMC before removing it. RAID 0 provides no fault
tolerance by itself, so when you power off the drive, the data on the storage system is lost. Therefore,
if you need to replace a disk in a RAID 0 configuration, we need to do this:

• All volumes and snapshots have a Network RAID level that provides redundancy across storage
systems. Any level other than Network RAID-0 provides this kind of redundancy.
• If volumes or snapshots are not protected (they are configured for Network RAID 0), change
them to a Network RAID level that provides data protection. You will have to wait for the data
to restripe, which could take some time.
• If the cluster does not have enough space for changing the Network RAID level, take a backup
of the volumes or snapshots and then delete them from the cluster.
After the disk replacement is complete, you can recreate the volumes and restore the data
from the backup.
• All volumes and snapshots show a status of Normal.
• Any volumes or snapshots that are being deleted have finished deleting.

Replacing a disk in RAID 0 on P4000

Complete the following checklist for single disk replacement RAID 0.

Manually power off the disk in the CMC for RAID 0
First power off the disk you are replacing in the CMC, which causes RAID to go off.

1. In the navigation window, select the storage system containing the disk to be replaced.
2. Select the Storage category.
3. Select the Disk Setup tab.
4. Select the disk in the list to power off.
5. Click Disk Setup Tasks, and select Power Off Disk.
6. Click OK on the confirmation message.

I hope this answers the question.

[bublik]

the hardware RAID on lefthand is RAID5 so there should be a protection from disk failuer. I understand that if I lose my node then all volumes will not be available but since hardware RAID is protected should it protect my data?

[Emilo]

Hello,

The P4000 provides to levels of RAID.

Unless you changed the default you will 12 drives with 3 logical drives on each P4500.

Logical drive 1 will be a hardware raid 10 that contains the OS it is stripped and mirrored accross the first 6 drives.

Logical drive 2 is a  HW RAID 5 stripped accross dirves 1-6

Logical drive 3 is HW RAID 5 stripped accross drives 7-12

So you could loose a drive in logical drive 2 and still be ok

You also could loose a drive in logical drive 3 at the same time and still be ok

Sceniaros where you would have a total loss of your cluster with Network RAID 0

You loose 2 drives on logical drive 1 , 2 or 3 on any node in the cluster.

Even though you might feel that you are willing to accept the risk loosing 2 drives in a array is more common then you think (power outages, accidently pulling the wrong drive etc).

If you value your data you get the best perfomance and redundancy by going with the reccomended

Hard RAID 5

Network RAID 10

Your other options are are

Hard RAID 6 allows you to loose 2 drives in each logical array

Network RAID 0 very fast

This option does decrease perfomance a bit and takes up more space. You had the double write on parity and if you loose a drive it takes longer to rebuild.

--------------------------------------

Hardware RAID 5

Network RAID 5 allows you to loose one entire node and still maintain your data. This option does have a slight decrease in performance and you need at least 3 nodes in the cluster. This option is only reccomended for archive and volumes that you will be performing mostly reads on.

Conclusion?

If your data is important to you go witht the default

HW RAID 5

Network RAID 10

It provides a good balacne of protection and performance.