NetScaler SDX 14000, 15000,16000, 25000 and 26000 series of platforms support RAID managed by the software. Multiple disks provide not only performance gains, but also enhanced reliability. Reliability is especially important for a NetScaler SDX appliance, because the appliance hosts a large number of virtual machines, and a disk failure affects multiple virtual machines. Service Virtual Management (SVM) supports RAID 1 configuration, which implements disk mirroring. That is, two disks maintain the same data. If a disk in the RAID 1 array fails, its mirror immediately supplies all the needed data.

RAID 1 disk mirroring combines two physical drives in one logical drive. The usable capacity of a logical drive is equivalent to the capacity of one of its physical drives

The SDX appliance in its default configuration is shipped with four disk slots populated with solid-state drives (SSDs). It includes the logical drive 0, which is allocated for the Management Service and XenServer, and logical drive 1, which is allocated for NetScaler instances that a user will provision. Disks in slots 1 and 2 create a RAID 1 pair for logical drive 0. Similarly, disks in slots 3 and 4 create a RAID 1 pair for logical drive 1. For additional storage as dictated by model number, license and capacity requirements, you can create additional new logical drives. This requires populating physical drives to form RAID 1 pairs in slots 5 and 6, and/or slots 7 and 8.

Viewing Drive Properties and Operations

A NetScaler SDX appliance supports a maximum of eight physical-drive slots. You can insert physical drives into the slots. Before you can use a physical drive, you must make it part of a logical drive needed.

In the Management Service, the Configuration > System > RAID screen includes tabs for storage repositories, logical drives, and physical drives.

Storage Repository

On the Configuration > System > RAID > Storage Repository tab, you can view the status of storage repositories on the NetScaler SDX appliance. The Storage Repository tab displays the following information about each storage repository:

• Name—Name of the storage repository drive.

• Size—Size of the storage repository.

• Utilized—Amount of storage-repository space in use.

Logical Drives

The RAID state of logical volume at times may reflect combination of above states as below:

clean, degraded
Applies to a degraded RAID 1 where one of the drives has failed or is offline
active, degraded
Applies to a degraded RAID 1 where one of the drives has failed or is offline
active, degraded, resyncing
Applies to a degraded RAID 1, where data on both the drives is in the process of being synchronized.
clean, degraded, recovering
Applies to a degraded RAID 1, where a new drive is being filled up with all the relevant data.
You can also view the details of the physical drives associated with the logical drive by selecting the logical drive and clicking the “Show Physical Drives” button.

Physical Drives 

Navigate to Configuration > System > RAID > Physical Drives tab, to view the following information:

• Slot - Physical slot associated with the physical drive.         
• State - Indicates if a physical drive is present on the appliance.
• Present - Physical drive is present on the appliance. 
• Not Present - It means either the physical drive is absent on the appliance or it has been deactivated so that it can be removed. 
• Size - Size of the physical drive.
• RAID State – Raid state of the physical drives.
  • active, sync  - Physical drive in good condition in sync with pending writes.
  • clean, sync   - Physical drive in good condition in sync with no pending writes.
  • spare, rebuilding – A new physical drive is being filled up with relevant data.
  • faulty – Physical drive in a faulty state.

In the Physical Drives pane, you can perform the following actions on the physical drives:

• Rebuild - Initiate a rebuild of the drive. When a drive in RAID 1 fails, you can rebuild the RAID 1 pair, by providing Citrix Certified disk and selecting this option.
  • Locate - Locate the drive on the appliance. Once the drive is located, the activity LED associated with the drive starts to blink.
  • Stop Locate - Stop locating the drive on the appliance.
  • Prepare to Remove - Deactivate the selected physical drive so that it can be removed.

Adding One Additional Logical Drive

1. On the back of the appliance, insert the two blank SSDs of same capacity in slot numbers 5 and 6. You can add the SSDs in a running system.

 Note: Make sure that the SSDs are Citrix certified.

2. In the Management Service, navigate to Configuration > System > RAID and the Physical Drives tab. You can see the SSDs that you added.
3. Navigate to the Logical Drives tab and click Create.
4. In the Create Logical Disk dialog box, select 5 and  6 and click Create.
5. The logical drive with name md_d2 is created and is listed under the Logical Drive tab. Click the refresh icon to update the order of the logical drives.

Note: A Force Clean Physical Disks  check option is available to erase any existing RAID metadata on the drives.

The drive is considered as a foreign drive if it came from another RAID setup or has old RAID metadata that needs to be erased. 

6.The logical drive with name md_d2 is created and is listed under the Logical Drives tab.

Adding Second Additional Logical Drive on the SDX Platform: 

1. To add another logical drive, insert the SSDs in slots 7 and 8 at the back of the appliance and follow the instructions above. 
2. In the Create Logical Disk dialog box,  select 7 and 8 and click Create button.
3. The logical drive with name md_d3 is created and is listed under the Logical Drives tab. 

Replacing a Failed or Defective SSD Drive with a Blank SSD Drive

To replace a defective SSD drive with a blank SSD drive:

1. In the Management Service, navigate to Configuration > System > RAID.
2. On the Physical Drives tab, select the defective drive that you want to replace.
3. Click Prepare to Remove to trigger the removal of the drive.
4. Click Physical Drives, the state of the drive should appear as Not Present.
5. Physically remove the defective drive from the slot.
6. Insert the new Citrix certified SSD in the slot from where you removed the defective SSD.
7. Click on refresh icon for the list of physical drives. The state of the drive should appear as Present.
8. Select the drive first and then click the Rebuild option. First, “Rebuild Physical   Drive” dialog box will be displayed, where user will need to click “OK”.

Note: A Force Clean check option is available in Rebuild Physical Drive  dialog box to erase any existing RAID metadata on the drive. The drive is considered as a foreign drive if it came from another RAID setup or has old RAID metadata that needs to be erased.

Replacing a Failed RAID logical Drive with two blank SSD Drives

In the case of an unfortunate event of VPX-SR failure, where both the drives that form a RAID1 pair have failed, it will be necessary to replace both the SSD drives. The procedure is similar to adding a logical drive as described in one of the above sections, however it does require few additional steps before creating a new logical drive.

This procedure requires the user to do the following:

1. Under the Management service NetScaler tab, select and delete each of the VPX instances residing on the failed VPX-SR.
2. Navigate to Logical Drives tab, select the failed “md_dX” and click Delete.
3. Replace the failed drives with new Citrix certified SSD drives in the corresponding slot pair.
4. Select the “md_dX” again, and click Create.

The logical drive with name “md_dX” is re-crated and ready for use. The VPX instances that were deleted earlier can now be created or restored as required.

On the Configuration > System > RAID > Logical Drives tab, you can view the name, state, size of each logical drive, and information about its component physical drives.