Storage FAQ
Do your units support the latest 2TB SATA II hard drives?
Yes. Sans Digital recommend RAID edition or Enterprise level hard drives for RAID application. For detail information, please contact Sans Digital Technical Support group.
What are the transfer rates/speeds of different connections?
USB2.0
480 Mbps
Firewire400/IEEE1394a
400 Mbps
Firewire800/IEEE1394b
800 Mbps
SATA I
1.5 Gbps
SATA II
3 Gbps
SCSI U320
320MBps
Fiber Channel
2/4Gbps
What is "RAID"?
RAID stands for "Redundant Array of Inexpensive Disks". The concept of RAID originated from a paper ("A case for Redundant Arrays of Inexpensive Disks" - 1987) published from the University of California at Berkley, proposing that using multiple small and rather inexpensive disks to replace the use of a single large disk to achieve fault-tolerant data redundancy. Another term "Parity Data" was often mentioned together with RAID. The parity data or disk is used to reconstruct data to a failed drive by comparing the data for the remaining drives in the array.
What are RAID levels?
Originally five RAID configurations, levels 1 through 6, were defined. A newer version, "data striping", or level 0, offers some performance advantages over other RAID levels but no data redundancy, so technically it isn't actually RAID. The most popular RAID levels are 0, 1, 3, 5 and 6, their definition of RAID levels are:
RAID 0
Known as disk striping. High Performance but no protection. It combines disks into one RAID that are used to improve some performance, but there is no logic to protect/recover data. *Synchronized disks are used.
RAID 1
This is known as mirroring. Data is written to two different disks at the same time, and data can be read from either disk. This helps to protect the data. If one disk is defective, the unit can still read the data from the other disk.
RAID 3
Striping data over several disks. Provides performance and protection. One of the disks will be used as parity. Parity interleaves at byte level and is stored in a dedicated disk. *Synchronized disks are required.
RAID 5
Striping data and parity over several disks with no dedicated disk for parity.
RAID 6
For each data stripe, there are 2 different and separate parity bits stored on 2 different disks among the RAID array members. There are 2 separate hardware XOR engines to generate the 2 parity bits. There are 2 major reasons justifying the need for RAID-6.
* Synchronized disks - Multiple disks are being used to write a single file. This is a function of the disk controller.
RAID 0
Known as disk striping. High Performance but no protection. It combines disks into one RAID that are used to improve some performance, but there is no logic to protect/recover data. *Synchronized disks are used.
RAID 1
This is known as mirroring. Data is written to two different disks at the same time, and data can be read from either disk. This helps to protect the data. If one disk is defective, the unit can still read the data from the other disk.
RAID 3
Striping data over several disks. Provides performance and protection. One of the disks will be used as parity. Parity interleaves at byte level and is stored in a dedicated disk. *Synchronized disks are required.
RAID 5
Striping data and parity over several disks with no dedicated disk for parity.
RAID 6
For each data stripe, there are 2 different and separate parity bits stored on 2 different disks among the RAID array members. There are 2 separate hardware XOR engines to generate the 2 parity bits. There are 2 major reasons justifying the need for RAID-6.
* Synchronized disks - Multiple disks are being used to write a single file. This is a function of the disk controller.
What is "JBOD"?
JBOD stands for Just Bunch Of Disks. A group of disks configured in an enclosure that are not configured as a RAID for fault-tolerance. There is no redundancy of the hard drives (No-RAID) and there are just bunch of disks in the enclosure. The simplicity of JBOD makes it a good choice to increase the capacity of the system easily and economically.
What is an eSATA PM port?
An eSATA PM (Port Multiplier) port incorporates up to 5 individual SATA HDDs into one single eSATA interface to reduce individual eSATA port/cable for each HDD. Even though the PM port looks identical to a regular eSATA port, you will need to have SATA HBA (Host Bus Adapter) that support Port Multiplier function to take advantage of the PM port. Some motherboard has built-in eSATA port. However, it may or may not be compatible. For more information, please contact Tech Support.
What is a SAS Expander port?
A SAS Expander port allows one SAS Host Bus Adapter to be connected to a maximum of 128 devices in a daisy chain connectivity format utilizing Mini-SAS (SFF-8088) cables. SAS (Serial Attached SCSI) is an high performance protocol/standard that can reach a maximum bandwidth of 1200 MBp/sec making it extremely suitable for high speed DAS (Direct attached storage) between the Host computer and its storage system. You will need to connect the SAS expander port to a SAS HBA. SATA HBA will not be compatible with SAS expander interface.
What is a Software iSCSI Initiator?
An iSCSI initiator is a software utility that allows your host computer to utilize remote data storage devices via an Ethernet network. iSCSi device uses SCSI protocol over Ethernet to transfer data in blocks and provide high speed interface between the host computer and the target storage system. You can download Microsoft iSCSI initiator from Microsoft website at http://www.microsoft.com/.
What is MPIO?
MPIO (Multi-path IO) is a feature that allows user to simultaneous combining 2 or more interface ports together to simulate one single port with maximum amount of bandwidth. It is a feature used in some iSCSI and Fibre Channel devices.
What is Trunking?
Trunking is a feature supported by “manageable” Ethernet switch. By combining multiple Ethernet ports into one virtual high speed port which allows maximum aggregated speed to be achieved between two virtual Ethernet devices. A manageable Ethernet switch, however, is generally required to support this feature. Manageable switch allows user to log into the unit for configuration and maintenance purpose and is usually a layer 2 or 3 switch.
What is Clustering?
Clustering is a feature in some Window Server operating systems that allows two identical host computer systems to simultaneously access the same storage system to provide fault tolerance over host computers. In the event that one of the host computers fails, the other host computer will be able to continue access the same data storage unit minimizing system downtime. Please check with your host computer operating system to see if clustering is supported.
What is Server Virtualization?
Server virtualization is a revolutionary and environmentally-friendly concept of harnessing the un-tapped power of the new fast CPU (Dual, Quad-Core). Server virtualization operating system allows one powerful host computer to simulate 5, 10 or more computers by initially installing a server vitalization operating system such as VMWare ESXi, ESX, vSphere, Microsoft Hyper-V or Citrix Xenserver. Server virtualization allows company to reduce computer hardware purchase cost, cooling cost and at the same time provide an easy access to all servers for system configuration and maintenance. SansDigital provides a great selection of enterprise level iSCSI, Fibre Channel and DAS RAID storage system for your VMware storage needs.
Please email us at [email protected] if you still have any questions or want to learn more.