A volume group is a container for volumes with shared characteristics. A volume group has a defined capacity and RAID level. You can use a volume group to create one or more volumes accessible to a host. (You create volumes from either a volume group or a pool.)

A pool is a set of drives that is logically grouped. You can use a pool to create one or more volumes accessible to a host. (You create volumes from either a pool or a volume group.)

Pools can eliminate the need for administrators to monitor usage on each host to determine when they are likely to run out of storage space and avoid conventional disk resizing outages. When a pool nears depletion, additional drives can be added to the pool non-disruptively and capacity growth is transparent to the host.

With pools, data is automatically re-distributed to maintain equilibrium. By distributing parity information and spare capacity throughout the pool, every drive in the pool can be used to rebuild a failed drive. This approach does not use dedicated hot spare drives; instead, preservation (spare) capacity is reserved throughout the pool. Upon drive failure, segments on other drives are read to recreate the data. A new drive is then chosen to write each segment that was on a failed drive so that data distribution across drives is maintained.

Reserved capacity is the physically allocated capacity that stores data for copy service objects such as snapshot images, consistency group member volumes, and mirrored pair volumes.

The reserved capacity volume that is associated with a copy service operation resides in a pool or a volume group. You create reserved capacity from either a pool or volume group.

FDE/FIPS security refers to secure-capable drives that encrypt data during writes and decrypt data during reads using a unique encryption key. These secure-capable drives prevent unauthorized access to the data on a drive that is physically removed from the storage array.

Secure-capable drives can be either Full Disk Encryption (FDE) drives or Federal Information Processing Standard (FIPS) drives. FIPS drives have undergone certification testing.

A redundancy check determines whether the data on a volume in a pool or volume group is consistent. Redundancy data is used to quickly reconstruct information on a replacement drive if one of the drives in the pool or volume group fails.

You can perform this check only on one pool or volume group at a time. A volume redundancy check performs the following actions:

A pool is similar to a volume group, with the following differences.

The following examples describe why you would want to manually configure a pool.

Capacity alerts indicate when to add drives to a pool. A pool needs sufficient free capacity to successfully perform storage array operations. You can prevent interruptions to these operations by configuring SANtricity System Manager to send alerts when the free capacity of a pool reaches or exceeds a specified percentage.

You set this percentage when you create a pool using either the Pool auto-configuration option or the Create pool option. If you choose the automatic option, default settings automatically determine when you receive alert notifications. If you choose to manually create the pool, you can determine the alert notification settings; or if you prefer, you can accept the default settings. You can adjust these settings later in Settings › Alerts.

If you have created volumes on all available usable capacity, you might not be able to increase preservation capacity.

Preservation capacity is the amount of capacity (number of drives) that is reserved on a pool to support potential drive failures. When a pool is created, the system automatically reserves a default amount of preservation capacity depending on the number of drives in the pool. If you have created volumes on all available usable capacity, you cannot increase preservation capacity without adding capacity to the pool by either adding drives or deleting volumes.

You can change the preservation capacity from Pools & Volume Groups. Select the pool that you want to edit. Click View/Edit Settings, and then select the Settings tab.

SANtricity System Manager sets limits for how many drives you can remove from a pool.

The following media types are supported: Hard Disk Drive (HDD) and Solid State Disk (SSD).

In the Add Capacity dialog, not all drives are available for adding capacity to an existing pool or volume group.

Drives are not eligible for any of the following reasons:

To maintain shelf/drawer loss protection for a pool or volume group, use the criteria specified in the following table.

When creating pools and volume groups, make sure to balance the drive selection between the upper and lower drive slots.

For the EF600 and EF300 controllers, drive slots 0-11 are connected to one PCI bridge, while slots 12-23 are connected to a different PCI bridge. For optimal performance, you should balance the drive selection to include a roughly equal number of drives from the upper and lower slots. This positioning ensures that your volumes do not hit a bandwidth limit sooner than necessary.

To maximize the performance of a volume group, you must select the appropriate RAID level. You can determine the appropriate RAID level by knowing the read and write percentages for the applications that are accessing the volume group. Use the Performance page to obtain these percentages.

Data Assurance (DA) implements the T10 Protection Information (PI) standard, which increases data integrity by checking for and correcting errors that might occur as data is transferred along the I/O path.

The typical use of the Data Assurance feature will check the portion of the I/O path between the controllers and drives. DA capabilities are presented at the pool and volume group level.

When this feature is enabled, the storage array appends error-checking codes (also known as cyclic redundancy checks or CRCs) to each block of data in the volume. After a data block is moved, the storage array uses these CRC codes to determine if any errors occurred during transmission. Potentially corrupted data is neither written to disk nor returned to the host. If you want to use the DA feature, select a pool or volume group that is DA capable when you create a new volume (look for "Yes" next to "DA" in the pool and volume group candidates table).

Make sure you assign these DA-enabled volumes to a host using an I/O interface that is capable of DA. I/O interfaces that are capable of DA include Fibre Channel, SAS, iSCSI over TCP/IP, NVMe/FC, NVMe/IB, NVME/RoCE and iSER over InfiniBand (iSCSI Extensions for RDMA/IB). DA is not supported by SRP over InfiniBand.

Drive Security is a feature that prevents unauthorized access to data on secure-enabled drives when removed from the storage array. These drives can be either Full Disk Encryption (FDE) drives or Federal Information Processing Standard (FIPS) drives.

Typically, you should increase capacity when you receive a warning that the reserved capacity is in danger of becoming full. You can increase reserved capacity only in increments of 8 GiB.

For snapshot operations, reserved capacity is typically 40 percent of the base volume. For asynchronous mirroring operations reserved capacity is typically 20 percent of the base volume. Use a higher percentage if you believe the base volume will undergo many changes or if the estimated life expectancy of a storage object's copy service operation will be very long.

You can decrease reserved capacity only by the amount you used to increase it. Reserved capacity for member volumes can be removed only in the reverse order they were added.

You cannot decrease the reserved capacity for a storage object if one of these conditions exists:

You can remove volumes for reserved capacity only in the reverse order that they were added.

You cannot decrease the reserved capacity for a snapshot volume that is read-only because it does not have any associated reserved capacity. Only snapshot volumes that are read-write require reserved capacity.

Each member volume in a snapshot consistency group must have its own reserved capacity to save any modifications made by the host application to the base volume without affecting the referenced consistency group snapshot image. Reserved capacity provides the host application with write access to a copy of the data contained in the member volume that is designated as read-write.

A consistency group snapshot image is not directly read or write accessible to hosts. Rather, the snapshot image is used to save only the data captured from the base volume.

During the creation of a consistency group snapshot volume that is designated as read-write, System Manager creates a reserved capacity for each member volume in the consistency group. This reserved capacity provides the host application with write access to a copy of the data contained in the consistency group snapshot image.

You can view nominal statistics and detailed statistics for SSD Cache. Nominal statistics are a subset of the detailed statistics.

The detailed statistics can be viewed only when you export all SSD statistics to a .csv file. As you review and interpret the statistics, keep in mind that some interpretations are derived by looking at a combination of statistics.

SSD drives will have longer life and better maximum write performance when a portion of their capacity is unallocated.

For drives associated with a pool, unallocated capacity is comprised of a pool's preservation capacity, the free capacity (capacity not used by volumes), and a portion of the usable capacity set aside as additional optimization capacity. The additional optimization capacity ensures a minimum level of optimization capacity by reducing the usable capacity, and as such, is not available for volume creation.

When a pool is created, a recommended optimization capacity is generated that provides a balance of performance, drive wear life, and available capacity. The Additional Optimization Capacity slider located in the Pool Settings dialog allows adjustments to the pool's optimization capacity. Adjusting the slider provides for better performance and drive wear life at the expense of available capacity, or additional available capacity at the expense of performance and drive wear life.

SSD drives will have longer life and better maximum write performance when a portion of their capacity is unallocated.

For drives associated with a volume group, unallocated capacity is comprised of a volume group's free capacity (capacity not used by volumes), and a portion of the usable capacity set aside as optimization capacity. The additional optimization capacity ensures a minimum level of optimization capacity by reducing the usable capacity, and as such, is not available for volume creation.

When a volume group is created, a recommended optimization capacity is generated that provides a balance of performance, drive wear life, and available capacity. The Additional Optimization Capacity slider in the Volume Group Settings dialog allows adjustments to a volume group's optimization capacity. Adjusting the slider provides for better performance and drive wear life at the expense of available capacity, or additional available capacity at the expense of performance and drive wear life.

Resource Provisioning is a feature available in the EF300 and EF600 storage arrays, which allows volumes to be put in use immediately with no background initialization process.

A resource-provisioned volume is a thick volume in an SSD volume group or pool, where drive capacity is allocated (assigned to the volume) when the volume is created, but the drive blocks are deallocated (unmapped). By comparison, in a traditional thick volume, all drive blocks are mapped or allocated during a background volume initialization operation in order to initialize the Data Assurance protection information fields and to make data and RAID parity consistent in each RAID stripe. With a resource provisioned volume, there is no time-bound background initialization. Instead, each RAID stripe is initialized upon the first write to a volume block in the stripe.

Resource-provisioned volumes are supported only on SSD volume groups and pools, where all drives in the group or pool support the NVMe Deallocated or Unwritten Logical Block Error Enable (DULBE) error recovery capability. When a resource-provisioned volume is created, all drive blocks assigned to the volume are deallocated (unmapped). In addition, hosts can deallocate logical blocks in the volume using the NVMe Dataset Management command or the SCSI Unmap command. Deallocating blocks can improve SSD wear life and increase maximum write performance. The improvement varies with each drive model and capacity.

Resource Provisioning is a feature available in the EF300 and EF600 storage arrays, which allows volumes to be put in use immediately with no background initialization process.

A resource-provisioned volume is a thick volume in an SSD volume group or pool, where drive capacity is allocated (assigned to the volume) when the volume is created, but the drive blocks are deallocated (unmapped). By comparison, in a traditional thick volume, all drive blocks are mapped or allocated during a background volume initialization operation in order to initialize the Data Assurance protection information fields and to make data and RAID parity consistent in each RAID stripe. With a resource provisioned volume, there is no time-bound background initialization. Instead, each RAID stripe is initialized upon the first write to a volume block in the stripe.

Resource-provisioned volumes are supported only on SSD volume groups and pools, where all drives in the group or pool support the NVMe Deallocated or Unwritten Logical Block Error Enable (DULBE) error recovery capability. When a resource-provisioned volume is created, all drive blocks assigned to the volume are deallocated (unmapped). In addition, hosts can deallocate logical blocks in the volume using the NVMe Dataset Management command or the SCSI Unmap command. Deallocating blocks can improve SSD wear life and increase maximum write performance. The improvement varies with each drive model and capacity.

Resource provisioning is enabled by default on systems where the drives support DULBE. You can disable that default setting from Pools & Volume Groups.