## SME Disk Architecture

The SME Disk feature encrypts the data contained in a disk.

The software architecture for the SME Disk is similar to the existing SME infrastructure that supports the SME tape. Disk support has been added to the existing SME architecture from MDS NX-OS Release 5.2.1. Figure 1-6 depicts a typical dual-fabric production data center. The SME disk functionality is provided on the following Cisco MDS hardware:

• 16-Port Storage Services Node (SSN-16) Module

• 18/4 Multiservice Module (MSM-18/4)

• 9222i Switch

Figure 1-6 shows the SME Disk architecture.

Figure 1-6 SME Disk Architecture

In the figure, a switch is termed as an SME node. A module has one or more interfaces that support SME. The SME nodes encrypt and decrypt the traffic flowing between the host and the storage. The Fibre Channel traffic to be encrypted or decrypted is directed to the SME node through the FC-Redirect feature of the SAN. For example, the SSN-16 can support 4 SME interfaces and the MSM-18/4 supports 1 SME interface.

SME Disk functionality works in the dual-fabric topology, where it performs encryption and decryption on all the paths present between the host and the storage.

Caution SME Disk does not support thin provisioning of disks.

SME Disk needs to manage all the paths to the disk in both the fabrics. An SME cluster provides this functionality. An SME cluster consists of a collection of SME nodes. Any SME node that fails in a cluster triggers another node in the same cluster to take control of the encryption and/or decryption activity.

The disk on which the SME Disk provides the encryption and/or decryption functionality can be the one without any existing data or the one with existing data. If the disk has existing data, the existing data needs to be encrypted. The process of converting the existing clear data to encrypted data is termed as data preparation.

Data preparation can be performed in offline mode. In the offline data preparation mode, the application on the host accessing the disk is quiesced and no I/Os are sent to the disk. SME Disk functionality also ensures that if any host tries to read or write the data from or into the disk, the particular I/O is failed back to the host.

In the Online Mode, the application on the host can continue to perform I/O on the disk while SME is converting the existing data on the disk from clear text to encrypted text.

The disk is uniquely identified in configuration by the cluster name, disk group name, and disk name.

For the purpose of encryption or decryption, the SME Disk requires encryption keys. For every encrypted disk, a key is generated. The SME’s existing Key Management Center (KMC) infrastructure is used for SME disk key management. Keys for each disk are generated by the Storage Media Encryption coprocessor and are stored in the SME Key Management Center.

Caution SME Disk does not allow dynamic resizing of LUN.
For Release 5.2.1, the maximum supported disk size is one block less than two terabyte (TB). The maximum LBA is 0xFFFFFFFE.
From Release 5.2.6, the supported disk size for signature and nonsignature mode clusters is greater than two TB.
SME Disk only supports disk block size of 512 bytes.
For Release 5.2.1, SME Disk does not support online conversion of existing clear data on the disk to encrypted data.