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How to implement RAID 0/1 using USB 3.0

Posted: 26 Jun 2014  Print Version  Bookmark and Share

Keywords:Universal Serial Bus  USB 3.0  redundant array of inexpensive disks  RAID  Server virtualisation 

Introduced in 2008, USB 3.0 is the third major version of the Universal Serial Bus (USB) interface for computer connectivity. USB 3.0 adds a new transfer mode called "SuperSpeed" capable of transferring data up to 5 Gbit/s. (For reference, USB 2.0's top transfer speed is 480 Mbit/s.)

USB 3.0 provides an alternative redundant array of inexpensive disks (RAID) implementation for applications like server virtualisation that have relatively less data to handle.

Server virtualisation is the process of creating multiple virtual servers from a single physical server. The benefits of server virtualisation are well established in the industry today and can be summarised as follows:
 • Lower IT asset cost
 • Reduced energy consumption
 • Lower operational costs
 • Less real estate required (i.e., the real estate required to accommodate multiple physical servers)

Server virtualisation requires virtualisation software based on a hypervisor that serves as a platform for the multiple operating systems running on the multiple virtual servers created. It is important to ensure that the hypervisor runs on a fast dedicated boot disc to reduce boot time. The boot disc is typically separated from the main storage in a server.

The boot disc configuration: RAID 0 or RAID 1
Hypervisor data has to be kept separate from the main storage in a server. It is common to use two disks to store hypervisor data in order to attain higher reliability and availability for the hypervisor boot image.

The two disks containing hypervisor data are combined in a RAID scheme. These disks are connected to a RAID controller that, in turn, communicates with the Platform Control Hub (PCH) of the server.

The RAID level can be either RAID 0 or RAID 1:

RAID 0: Virtualisation data is interleaved between the two disks (striped). This improves performance but provides no tolerance to faults (i.e., any disc failure causes the storage array to break down).

Figure 1: Basic RAID 0 configuration.

RAID 1: Data is written identically to the two disks (mirrored). Both disks service read requests, and write requests update both disks. Thus, RAID 1 provides tolerance to single disc fault.

Figure 2: Basic RAID1 configuration.

Traditional implementation
A traditional RAID implementation (figure 3) requires the following components:
 • RAID controller for controlling the disks with hypervisor data and also for communication with the PCH of the server
 • SAS or SATA drives for storing hypervisor data

Figure 3: A traditional RAID implementation.

The RAID controller manages the physical drives (in this case, the SAS/SATA drives storing hypervisor data) and presents them as logical units to the computer's host adapter. The RAID controller provides two interfaces:
 • Back-end Interface: Communicates with the controlled disks. The protocol used is usually ATA, SATA, SCSI, FC, or SAS
 • Front-end Interface: Communicates with the host adapter. The protocol may be the same as that of the back-end interface or different.

In terms of its architecture, this implementation assures good performance. However the question remains whether this approach can meet application requirements while achieving price optimisation.

A RAID controller is useful for handling terabytes of data, as per the need of traditional RAID applications to connect individual SAS/SATA drives, each containing a large volume of data. In the case of virtualisation, the hypervisor images are typically 3-4 GB. Hence, using a traditional RAID controller with SAS/SATA drives is overkill. Moreover, SAS and SATA drives consume a lot of power and occupy significant board space.

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