As you might now, MegaCLI is the command line interface application for managing LSI MegaRAID family of hardware RAID controllers. It is very powerful, yet many times cumbersome, due to its award set of flags and options. You can find a large number of documentation about MegaCLI, from an official manual to cheat sheets and wikis.
I’ve seen plenty of information on how to create new arrays, with or without hot spare drives. However I haven’t find any that says what to do when you add a new disk to a enclosure, how to make it a hot spare for a preexistent array. This is what this post is about. I’ll tell you, it was a little tricky.
Before we begin, you should be familiar with the terms enclosure and slot. Enclosure is a chassi where disks are installed. They are enumerated because a single MegaRAID adapter may controls a number of them. Slot is simply a space in the enclosure where you physically install a disk. Thus, the slot ID is used interchangeably as a disk ID. You will see all the time in documentation the identifier [E:S]. This is simply referencing to a disk in slot S, installed in the enclosure E.
All shell commands here were executed as root, indicated by the prompt symbol #. In the system I am working on the enclosure ID is 252.
Let’s say we have a preexistent RAID-5 with 6 disks (from slot 0 to 5), and you just installed a brand new disk in slot 6. By the way, good practices suggest that the new disk should have the same model/capacity of others. If not possible, the new disk must have at least the same capacity of the largest one.
Once you connected the new disk it will be available as a JBOD disk. This means it has no relationship with any other RAID in the system. Using the following command you can see the current Firmware state property:
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# megacli -PDInfo -PhysDrv [252:6] -a0
Enclosure Device ID: 252
Slot Number: 6
[....]
PD Type: SAS
Raw Size: 1.819 TB [0xe8e088b0 Sectors]
Non Coerced Size: 1.818 TB [0xe8d088b0 Sectors]
Coerced Size: 1.818 TB [0xe8d00000 Sectors]
Sector Size: 512
Logical Sector Size: 512
Physical Sector Size: 512
Firmware state: JBOD
Port's Linkspeed: 6.0Gb/s
[...]
Drive has flagged a S.M.A.R.T alert : No
Surprisingly enough, in my experimentations the controller does not apply any further configuration on a disk with a state JBOD. That is annoying because JBOD term alludes that disk may used as a standalone disk, and since disk is not marked as bad you could use it right away.
So, here comes the trick. You might change the firmware state to Unconfigured-Good using the -PDMakeGood option. After the controller set disk as good, it spins disk up making the disk ready for any usage.
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# megacli -PDMakeGood -PhysDrv [252:6] -Force -a0
Adapter: 0: EnclId-252 SlotId-6 state changed to Unconfigured-Good.
Exit Code: 0x00
root@kanar:~# megacli -PDInfo -PhysDrv [252:6] -a0
Enclosure Device ID: 252
Slot Number: 6
[...]
PD Type: SAS
Raw Size: 1.819 TB [0xe8e088b0 Sectors]
Non Coerced Size: 1.818 TB [0xe8d088b0 Sectors]
Coerced Size: 1.818 TB [0xe8d00000 Sectors]
Sector Size: 512
Logical Sector Size: 512
Physical Sector Size: 512
Firmware state: Unconfigured(good), Spun Up
[...]
Exit Code: 0x00
Exit Code: 0x00 means the operation was completed successfuly.
Finally, you can set the new disk as hot spare. In this example, it will be a global hot spare, meaning that it will replace faulty disk from any RAID. MegaRAID also supports dedicated hot spare, which as it sounds is dedicated to a particular array.
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# megacli -PDHSP -Set -PhysDrv [252:6] -a0
Adapter: 0: Set Physical Drive at EnclId-252 SlotId-6 as Hot Spare Success.
Exit Code: 0x00
At the end, you can check the new disk hot spare status:
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# megacli -PDInfo -PhysDrv [252:6] -a0
Enclosure Device ID: 252
Slot Number: 6
[...]
PD Type: SAS
Hotspare Information:
Type: Global, is revertible
Raw Size: 1.819 TB [0xe8e088b0 Sectors]
Non Coerced Size: 1.818 TB [0xe8d088b0 Sectors]
Coerced Size: 1.818 TB [0xe8d00000 Sectors]
Sector Size: 512
Logical Sector Size: 512
Physical Sector Size: 512
Firmware state: Hotspare, Spun Up
[...]
Port's Linkspeed: 6.0Gb/s
Drive has flagged a S.M.A.R.T alert : No
Exit Code: 0x00
Note the Type: Global, is revertible property. Being reversible means that in the case the hot spare is active with a copy of a faulty disk, when you replace the faulty disk, the controller will copy data from the hot spare to the new disk and will make the hot spare be back to its original hot spare status.
In this post we discussed a simple, but not very documented, way to configure a newly added disk as a hot spare on a MegaRAID controller using MegaCLI.
Bye for now!