How to: Universal Hot-spare Management for ZFS-based Storage Pools

A standard best practice for preventing data loss due to disk failure is to designate one or more disk spares so that fault-tolerant arrays can auto-heal using the spare in the event of a HDD or SSD drive failure.  Universal hot-spare management takes that a step further and lets you repair any array in the system with a given hot-spare rather than having to designate specific spares for specific RAID groups (arrays).

Policy Driven Hot Spare Management

QuantaStor’s universal hot-spare management was designed to automatically or manually reconstruct/heal fault-tolerant arrays (RAID 1/10/5/50/6/60/7/70) when one or more disks fail.  Depending on the specific needs of a given configuration or storage pool, spare disk devices can be assigned to a specific pool or added to the “Universal” hot spare list meaning that it can used by any storage pool.

QuantaStor’s hot spare management system is also distributed and “grid aware” so that spares can be shared between multiple appliances if they are connected to one or more shared disk enclosures (JBODs).  The grid aware spare management system makes decisions about how and when to repair disks pools based on hot-spare management policies set by the IT administrator.

Some of the challenges that the QuantaStor’s policy driven auto-heal system must tackle includes making sure to only repair pools with like devices (don’t use that slow HDD to repair an SSD pool!), detecting when an enclosure was turned off by differentiating between a power loss versus a disk failure, allowing users to set policies and designate disks to pools as needed and allowing hot spares to be shared and reserved within and across appliances for HA (High Availability) configurations.

With this policy driven hot-spare management, OSNEXUS has developed an advanced system that makes managing HBA (SAS Host Bus Adapter) connected spares for our ZFS-based Storage Pools as easy as managing spares in a hardware RAID controller (also manageable via QuantaStor).

Configuring Storage Pool Hot Spare Policies

The Hot Spare Policy Manager can be found in the Modify Storage Pool dialog box under Storage Pools. (Figure 1)

QuantaStor Hot Spare Policy Manager

Figure 1

The default hot spare policy is “Autoselect best match from assigned or universal spares.” Additional options include auto-select best match from pool assigned spares only, auto-select exact match from assigned or universal spares, auto-select exact match from pool assigned spares only and manual hot spare management only.

Marking Hot-Spares

Marking and unmarking physical disks as hot spares can be found under “Physical Disks” by clicking on the disk and then selecting from the dialog box “Mark as Hot Spare” or “Unmark as Hot Spare.” This applies to the “Universal” hot spare list. (Figure 2)

Figure 2Figure 2

Pinning Spares to Specific Storage Pools

To add assigned disk spares to specific storage pools rather than the universal spare list click on the storage pool and select “Recover Storage Pool/Add Spares.” (Figure 3)

Adding Assigned Disk Spares to Specific Storage Pools
Figure 3

Select disks to be added to the storage pool using the “Add Hot-spares / Recover Storage Pool” dialog box. (Figure 4)

Add Hot-spares / Recover Storage Pool
Figure 4 

For more information about Hot Spare Management and Storage Pool Sizing see the OSNEXUS Solution Design Guide.

Categories: Disaster Recovery


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