DiscounTechnology Blog

Serial Attached SCSI (SAS) is becoming the new storage standard in the corporate environment. Being new, SAS brings many questions to the mind of IT Managers and others. This FAQ will attempt to answer the most common of these questions.

What is SAS (Serial Attached SCSI)?

Serial Attached SCSI (SAS) is an evolution of SCSI to a much faster serial interface. This satisfies the enterprise storage requirement of scalability, performance, reliability and manageability. It also provides an infrastructure for both SAS drives and SATA disk drives. Since the SAS interface is compatible with SATA devices, this provides users with almost unlimited choices for server and storage systems structure. SAS drives, with their outstanding speed and reliability can be used for critical online storage while SATA drives, with their higher capacity and significantly lower cost, can be used for less critical storage requirements.

Why was Serial Attached SCSI developed?

SAS was developed to solve future direct attach storage requirements. It provides compatibility with SATA and offers compatibility with SCSI as well as SCSI reliability, performance and manageability.

Aren't parallel interfaces faster than serial interfaces?

Previously, parallel interfaces were preferable to serial because their multiple data paths allowed for greater throughput than the single data path of serial interfaces. New developments in VLSI technology, however, have enabled serial interfaces to make dramatic speed increases. Serial interfaces do not have the complex timing and interference issues that hinder parallel interface development. Serial Attached SCSI features higher throughput and greater potential for advancement in the future as compared to parallel SCSI.

Is parallel SCSI now obsolete?

No. Parallel SCSI has played a fundamental role in enterprise data storage and will continue to do so. Serial Attached SCSI, however, is a strong complement to and matches the excellent reliability and robustness of parallel SCSI, while significantly expanding SCSI storage in terms of speed, scalability and flexibility. For instance, parallel development has stopped at 300GB SCSI hard drives while we already have in stock 450GB SAS drives and 1TB SAS drives are not far off.

Will migrating from parallel SCSI to SAS be difficult?

When Seagate and other companies collaborated to define Serial Attached SCSI standards, ease of migration was a primary consideration. SAS was engineered to be compatible with existing SCSI command sets thus preserving your investment in storage management and enterprise application software.

What is the difference between Serial Attached SCSI (SAS) and Serial ATA (SATA)?

Serial Attached SCSI is an enterprise storage solution that delivers the superior performance, reliability and scalability demanded in mission-critical applications. Serial ATA is primarily intended for desktop applications and suitable for use in low work load non-mission-critical environments where low cost is a high priority. This allows the development of tiered SAS and SATA storage environments where SAS is used for operating the mission-critical applications and SATA is used for providing huge amounts of storage at a low cost.

What are Small Form Factor SAS Drives?

Small form factor (SFF) 2.5 inch SAS enterprise hard drives are a new class of storage solution that feature a 70% smaller physically size and up to 40% less power consumption and heat generation while maintaining true enterprise level performance and reliability.

Because of their smaller size and lower power consumption, SFF drives have found applications in Blade Servers, storage consolidation and data center environments. SFF drives are available in capacities ranging from 36GB to 146GB with higher capacities on the horizon.

Years ago, adding a new devices to your PC was at times a nightmare. You had to manually configure resources such as interrupt levels and shared memory for each new device. Many times this created conflicts with existing devices that had to be resolved.

Along came Plug and Play (PnP) technology that changed all that and simplified adding new devices to your PC. PnP devices configured themselves by automatically adjusting their settings to work properly in your PC.

Universal Plug and Play (UPnP) does for your network what PnP did for your PC. UPnP makes adding a device to your network as simple as plugging it onto your network and turning it on.

A good example of such a device is the External 2-Bay Network Storage Enclosure DNS-323. The D-Link DNS-323 2-Bay Network Storage Enclosure, when used with internal SATA drives, enables you to share documents, files, and digital media such as music, photos, and video with everyone on the home or office network. Remotely accessing files through the Internet is also possible with the built-in FTP server2. Whether you are allowing access locally or over the Internet, keep data safe by only giving rights to specific users or groups. When configuring the DNS-323, you can create users and groups and assign them to folders with either read or read/write permissions.

How UPnP Works

When a device is first connected to a UPnP network, it must first obtain an IP address. This can be from the networks DHCP server or, if there is none, the device must self assign an IP to itself. Next, the device will advertise its presence on the network by providing a description of itself and the services it offers.

A control point receives this description which includes a list of actions related to each of the services the device is offering and information on the state of the device. The control point then send action requests to the device. The result of these requests are published on the network by event messages sent by a service on the device. If applicable, the control point will send a web page to the user's browser that will allow the user to manage the device and monitor its status.

Laptop hard drives have long been made to be very resistant to shock due to the nature of the environment they operate in. Seagate has now taken this one step further with their Free-Fall Protection. This feature provides enhanced data protection against shocks that the drive may endure while it is operating.

What is Free-Fall Protection?

Free-Fall Protection uses a zero G acceleration sensor mounted on the circuit board of the drive. This sensor detects any changes in acceleration of the drive, such as when it or the laptop it is mounted in is dropped. When a Free-Fall event is detected, the drive will cause the actuator to park the heads away from the surface of the platter thus preventing head / platter contact and the resultant loss of data. This protection can be engaged in a fall as little as 8 inches.

Drives With Free-Fall Protection

Seagate's Momentus 7200.2 line of drives are available in 80GB, 100GB, 120GB and 160GB capacities. They spin at 7200 rpm for outstanding performance and use perpendicular recording technology to achieve these high capacities in a 2.5 inch form factor. DiscounTechnology now carries these drives beginning with the ST980813ASG. This is an 80GB SATA drive that features Free-Fall Protection.

Fujitsu Europe has been offering the optional adding of a freefall sensor to its MHW2xxxBH drive series since April 2007.>/p>

When faced with the task of upgrading the amount of storage on your Sun server, two alternatives must be considered: Original Sun Hard Drives and Third Party Compatible Kits. DiscounTechnology carries both Sun Original Drives and Third Party Compatible Sun Hard Disk Kits. Third Party kits can be used in all Sun applications except the operating system boot drive where Sun requires a Sun original drive to be used.

Sun Original Drives

An Sun Original Drive, like the Original Sun XRA-SC1NB-146G15K SCSI Hard Drive, will be delivered in its individual box with the be the drive already mounted in its tray/caddy. An Sun Original Drive gives you 100% assured compatibility with the server it is designed for. The server's controller card will automatically recognize the drive as being of Sun manufacture and no controller settings need be altered. The downside of using Sun Original Drives is that they are considerably more expensive than Third Party Compatible Kits and may also be harder to obtain at times.

Third Party Compatible Kits

A Third Party Compatible Kit, like the Generic Sun XRA-SC1NB-146G15K SCSI Hard Drive Kit is delivered with the drive and tray/caddy packaged separately (screws included). A Third Party Compatible Kit is guaranteed to be compatible with the server it is designed for. The advantage of using Third Party Compatible Kits is that they are considerably less expensive and more readily available than Sun Original Drives.

Points to Consider with Sun Original Drives

• 100% guaranteed compatibility
• Considerably more expensive than Third Party Compatible Kits
• More Difficult to Obtain than Third Party Compatible Kits

Points to Consider with Third Party Compatible Kits

• Compatible with Sun Servers
• Less Expensive than Sun Original Drives
• More Readily Available than Sun Original Drives
• No performance difference compared to Sun Original Drives

Other Sun Hard Drives

The following are other Sun Hard Drives that DiscounTechnology stocks:

• Sun XTASC1NC300G10K SCSI Hard Drive
• Sun XTASC1NC146G10K SCSI Hard Drive
• Sun Generic XTASC1NC146G10K SCSI Hard Drive
• Sun Generic XTASC1NC300G10K SCSI Hard Drives
• Sun Generic XTASC1NC146G10K SCSI Hard Drives
• Sun Generic 540-6097 SCSI Hard Drive Kit
• Sun Generic 540-4520 SCSI Hard Drive Kit
• Sun Generic 540-4904 SCSI Hard Drive Kit
• Sun Generic 540-4263 SCSI Hard Drive Kit
• Sun Generic 540-6121 SCSI Hard Drive Kit
• Sun Generic 540-5455 SCSI Hard Drive Kit
• Sun Generic 540-5456 SCSI Hard Drive Kit
• Sun Generic 540-5771 SCSI Hard Drive Kit
• Sun Generic 540-5924 SCSI Hard Drive Kit
• Sun Generic 540-6449 SCSI Hard Drive Kit
• Sun Generic 540-6915 SCSI Hard Drive Kit
• Sun Generic 540-6057 SCSI Hard Drive Kit
• Sun Generic 540-6056 SCSI Hard Drive Kit
• Sun Generic 540-6936 SCSI Hard Drive Kit
• Sun Generic 540-6058 SCSI Hard Drive Kit
• Sun Generic 540-5735 SCSI Hard Drive Kit
• Sun Generic 540-6129 SCSI Hard Drive Kit
• Sun Generic 540-6494 SCSI Hard Drive Kit
• Sun Generic 540-6366 SCSI Hard Drive Kit
• Sun Generic 540-6064 SCSI Hard Drive Kit
• Sun Generic XRA-SC1NB-146G15K SCSI Hard Drive Kit
• Sun XRA-SC1NB-146G15K SCSI Hard Drive
• Sun 540-6458 SCSI Hard Drive

Extremely high through put data connections usually require a hard wired fiber optic connection. There are many instances were this is impractical, impossible or too expensive. Enter the wireless optical point to point data link. A good example of this is the LightPointe FlightStrata G Optical Gigabit Link.

Advantages

Speed	Full duplex Gigabit Ethernet (1.25Gbps) connectivity for data intensive networks
Reliability	Immune to interference Autotracking - Heads automatically adjust to keep beams aligned Four beam to four receiver connectivity
Security	Very narrow beams of invisible light that spread less than one half of a degree make detection and interception virtually impossible

Applications

Enterprise Connectivity

Many large companies occupy several buildings in the same vicinity and need to have high speed connectivity between them. The typical 1.54 Mb cable copper lines between buildings are too slow by several orders of magnitude. Running fiber optic lines would solve the problem but is extremely expensive. Wireless optical connectivity is the ideal solution providing secure and reliable Gigabit Ethernet speeds.

Disaster Recovery

Natural or man made disasters could result in fiber cuts resulting in disruption of connectivity between a corporations business assets. This is unacceptable and can result in huge financial losses when the flow of voice traffic and financial transactions is disrupted. Business can deploy wireless optical links both as a backup to fiber connections as well as to add bandwidth to the corporate network.

Video

Real time video monitoring networks are used in a variety of applications including warehousing, shipping harbors, mass transportation monitoring and street monitoring. These neworks require a bandwith much higher than the 1.5Mbps that T1 lines can provide. Deploying fiber optics would be unreasonably expensive. Wireless optical is the ideal solution providing secure and reliable connections up to gigabit speeds.

When faced with the task of upgrading the amount of storage on your HP server, two alternatives must be considered: HP Original Drives and Third Party Compatible Kits. DiscounTechnology carries both HP Original Drives and HP Third Party Compatible Kits.

HP Original Drives

An HP Original Drive, like the HP Original 286714-B22 SCSI Hard Drive, will be delivered in its individual box with the be the drive already mounted in its tray/caddy. An HP Original Drive gives you 100% assured compatibility with the server it is designed for. The server's controller card will automatically recognize the drive as being of HP manufacture and no controller settings need be altered. The downside of using HP Original Drives is that they are considerably more expensive than Third Party Compatible Kits and may also be harder to obtain at times.

Third Party Compatible Kits

A Third Party Compatible Kit, like the HP / Compaq Generic 286716-B22 SCSI Hard Drive Kit is delivered with the drive and tray/caddy packaged separately (screws included). A Third Party Compatible Kit is guaranteed to be compatible with the server it is designed for. The advantage of using Third Party Compatible Kits is that they are considerably less expensive and more readily available than HP Original Drives.

Points to Consider with HP Original Drives

• 100% guaranteed compatibility
• Considerably more expensive than Third Party Compatible Kits
• More Difficult to Obtain than Third Party Compatible Kits

Points to Consider with Third Party Compatible Kits

• Compatible with HP Servers
• Less Expensive than HP Original Drives
• More Readily Available than HP Original Drives
• No performance difference compared to HP Original Drives
• Server controllers might have to be configured to accept non HP Original Drives

Other HP Hard Drives

The following are other HP Hard Drives that DiscounTechnology stocks:

• HP Original 286714-B22 SCSI Hard Drive
• HP Original 286716-B22 SCSI Hard Drive
• HP Original 350964-B22 SCSI Hard Drive
• HP Original 286778-B22 SCSI Hard Drive
• HP Original 347708-B22 SCSI Hard Drive
• HP Original 411089-B22 SCSI Hard Drive
• HP Original 286776-B22 SCSI Hard Drive
• HP Original 286713-B21 SCSI Hard Drive
• HP / Compaq Generic 411089-B22 SCSI Hard Drive Kit
• HP / Compaq Generic 350964-B22 SCSI Hard Drive Kit
• HP / Compaq Generic 347708-B22 SCSI Hard Drive Kit
• HP / Compaq Generic 286714-B22 SCSI Hard Drive Kit
• HP / Compaq Generic 286716-B22 SCSI Hard Drive Kit
• HP / Compaq Generic 286778-B22 SCSI Hard Drive Kit
• HP / Compaq Generic 286776-B22 SCSI Hard Drive Kit

RAID is an acronym for Redundant Array of Independent (or Inexpensive) Disks. RAID arrays are used for two main purposes: fault tolerance and increased performance. There are many different levels of RAID functionality. All but one of the RAID levels provide varying degrees of data protection. Each of the RAID levels provides different performance levels during both normal (optimum) operation as well as during degraded (where a drive failure has been compensated for) operation.

What You Need to Build a RAID System

A RAID system requires two components: a RAID controller and at least the minimum number of hard drives required by the RAID level to be used. RAID systems can be built using SAS, SATA or SCSI hard drives.

There are many very capable SAS/SATA RAID controllers. Examples of several that we carry are: LSI Logic 8344ELP SAS / Serial Attached SCSI RAID Controller, Adaptec 4800SAS SAS Serial Attached SCSI 8 port RAID Controller and Dell XM768 UT568 RF480 PERC 5e 5/E SAS / Serial Attached SCSI RAID Controller.

Two very capable SCSI controllers are the Adaptec 2120S and the Dell PERC 4/DC.

RAID Operational States

A RAID system that has all its drives operating normally is said to be in an "Optimal" state. Most RAID levels, except for RAID 0, can tolerate the failures of some number of drives without data loss. That means that the RAID system will continue to operate and service I/O requests but is said to be operating in a "Degraded" state. It is essential that the failed drive in a degraded RAID be replaced as soon as possible since a second drive failure might cause data loss. Many RAID systems can be setup with a "hot spare". A hot spare is an extra drive that is operating but not used for data storage. The RAID controller will automatically replace a drive that failed with the hot spare. Once the failed drive has been replaced, the RAID controller will start to rebuild the data that was on the failed drive onto the replacement drive. This process may take quite some time and will cause substantially reduced through put from the array. The time that the rebuild is taking place also presents another vulnerability. The rebuild places the greatest stress on the RAID array due to the extremely high number of I/O operations taking place. A drive in the array that is already marginal, may fail during this rebuild.

RAID Levels

RAID 0 - Striping

RAID 0 writes out the blocks of each file across multiple hard drives. This level provides the highest read and write performance of any of the RAID levels but provides no fault tolerance; the failure of one drive will result in complete data loss. RAID 0 requires a minimum of two hard drives. RAID 0 also has no cost penalty associated with it since the total usable capacity of all the drives is available.

RAID 1 - Mirroring

RAID 1 delivers fault tolerance by keeping identical copies of your data on separate disk drives; should one drive fail, the system can continue to operate on the remaining drive, allowing the user time to replace the failed drive. Mirroring provides very high read performance but only medium write performance since there is overhead associated with writing duplicate copies of the data to separate drives. RAID 1 requires two hard drives and has a 50% cost penalty since the total usable capacity is that of a single drive.

RAID 5 - Striping with Parity

RAID 5 stripes data across multiple drives but provides fault tolerance by reserving the space equivalent to one drive for parity storage. RAID 5 can tolerate the failure of one drive in the set without any data loss. Read performance with RAID 5 is high but write performance is low due to the overhead of parity calculation and writing. RAID 5 requires a minimum of three hard drives and carries a space penalty equivalent to the capacity of one drive.

RAID 6 - Striping with Dual Parity

RAID 6 is similar to RAID 5 but requires an extra drive so that dual parity can be implemented. With dual parity, RAID 6 can tolerate the failure of two hard drives without data loss. Performance is the same as RAID 5 and a minimum of four drives are required. The space penalty is equivalent to the capacity of two drives.

RAID 10 - Striping and Mirroring

RAID 10 uses two or more RAID 1 mirror arrays and then does RAID 0 striping across these arrays. This provides the redundancy of mirroring and also the improved performance of striping. RAID 10 can tolerate a failure of one drive in each mirror sub-array without data loss. Read performance is high and write performance is medium. RAID 10 requires a minimum of four drives and has a space penalty of 50% of the total drive capacity.

RAID 50 - Striping Over RAID 5

RAID 50 uses two or more RAID 5 arrays and then does RAID 0 striping across them. This provides the fault tolerance of RAID 5 and also the improved performance of striping. RAID 50 can tolerate a failure of one drive in each sub-array without data loss. Read performance is high and write performance is medium. RAID 50 requires a minimum of six drives and has a space penalty of "n" drives where n is the number of sub-arrays.

RAID 60 - Striping Over RAID 6

RAID 60 uses two or more RAID 6 arrays and then does RAID 0 striping across them. This provides the fault tolerance of RAID 6's dual parity and also the improved performance of striping. RAID 60 can tolerate a failure of two drive6 in each sub-array without data loss. Read performance is high and write performance is medium. RAID 50 requires a minimum of eight drives and has a space penalty of "2n" drives where n is the number of sub-arrays.

RAID Level Performance and Comparison

Features	RAID 0	RAID 1	RAID 5	RAID 6	RAID 10	RAID 50	RAID 60
Minimum # of Drives	2	2	3	4	4	6	8
Fault Tolerance	None	Single Drive Failure	Single Drive Failure	Up to two Drive Failures	One drive failure in each sub array	One drive failure in each sub array	Up to two drive failures in each sub array
Read Performance	High	High	High	High	High	High	High
Write Performance	High	Medium	Low	Low	Medium	Medium	Medium
Read Performance (degraded)	n/a	Medium	Low	Low	High	Medium	Medium
Write Performance (degraded)	n/a	High	Low	Low	High	Medium	Low
Space Penalty	0%	50%	6% - 33%	12% - 50%	50%	6% - 33%	12% - 50%

When faced with the task of upgrading the amount of storage on your IBM server, two alternatives must be considered: IBM Original Drives and Third Party Compatible Kits. DiscounTechnology carries both IBM Original Drives and IBM Third Party Compatible Kits.

IBM Original Drives

An IBM Original Drive, like the IBM Original 40K1028 SCSI Hard Drive, will be delivered in its individual box which bears the IBM Logo/Hologram. Inside each box will be the drive already mounted in its tray/caddy. An IBM Original Drive gives you 100% assured compatibility with the server it is designed for. The server's controller card will automatically recognize the drive as being of IBM manufacture and no controller settings need be altered. The downside of using IBM Original Drives is that they are considerably more expensive than Third Party Compatible Kits and may also be harder to obtain at times.

Third Party Compatible Kits

A Third Party Compatible Kit, like the IBM 40K1025 SCSI Hard Drive Kit is delivered with the drive and tray/caddy packaged separately (screws included). An Third Party Compatible Kit is guaranteed to be compatible with the server it is designed for although some IBM controllers might need to be configured to accept non IBM drives transparently. The advantage of using Third Party Compatible Kits is that they are considerably less expensive and more readily available than IBM Original Drives.

Points to Consider with IBM Original Drives

• 100% guaranteed compatibility
• Server controllers automatically recognize the drives as IBM
• Considerably more expensive than Third Party Compatible Kits
• More Difficult to Obtain than Third Party Compatible Kits

Points to Consider with Third Party Compatible Kits

• Compatible with IBM Servers
• Less Expensive than IBM Original Drives
• More Readily Available than IBM Original Drives
• No performance difference compared to IBM Original Drives
• Server controllers might have to be configured to accept non IBM Original Drives

Other IBM Hard Drives

The following are other IBM Hard Drives that DiscounTechnology stocks:

• IBM Original 40K1023 SCSI Hard Drive
• IBM 40K1023 SCSI Hard Drive Kit
• IBM Original 40K1024 SCSI Hard Drive
• IBM 40K1024 SCSI Hard Drive Kit
• IBM Original 40K1025 SCSI Hard Drive
• IBM 40K1025 SCSI Hard Drive Kit
• IBM Original 40K1026 SCSI Hard Drive
• IBM 40K1026 SCSI Hard Drive Kit
• IBM 40K1027 SCSI Hard Drive Kit
• IBM Original 40K1028 SCSI Hard Drive
• IBM 40K1028 SCSI Hard Drive Kit

Solid state drives (SSD) are data storage devices that use either NAND flash (non-volatile) or SDRAM (volatile) memory to store persistent data. SSDs are available in 1.8", 2.5" and 3.5" form factors. Thus they emulate conventional hard disk drives and are plug compatible replacements.

Two Types of SSDs

SSDs are manufactured with either NAND flash (non-volatile) or SDRAM (volatile) memory modules.

The advantage of SSDs based on volatile SDRAM memory is their extremely fast data access - typically less than 0.01 milliseconds. This is over 200 times faster than the fastest hard drives in existence. One of their primary uses is to accelerate applications that would otherwise be bogged down by hard drive latency times.

DRAM-based SSDs volatility are also its disadvantage. Being volatile they must incorporate an internal battery and backup their data to a regular hard drive should a power failure occur. If power is lost and the battery should fail, all data would be lost.

Most SSDs are now manufacturered using non-volatile flash memory. These flash memory-based SSDs do not require batteries. This allows manufacturers to emulate standard disk drive form factors (1.8-inch, 2.5-inch, and 3.5-inch). Their nonvolatility allows flash based SSDs to retain memory even during sudden power outages. Flash based SSDs are also extremely fast compared to regular hard drives but are significantly slower than SDRAM SSDs.

The Advantages of SSDs

• Extremely low read and write latency times
• Faster startup since there is no drive spin-up time delay
• Faster random I/O compared to hard disk drives
• No moving parts resulting in higher reliability
• Lower power consumption and heat signature than hard drives

The Disadvantages of SSDs

• Cost per gigabyte is considerably higher than regular hard drives
• Slower random write speeds
• SSDs are more susceptible to magnetic fields and static charges
• Write cycles on SSDs are limited before the device wears out (100,000-5,000,000)

DELL Rail Kits

DELL supplies three types of rail kits for mounting DELL servers into a rack. Dell's rail kits will work only with DELL servers - no other brand of server is supported.

RAPID RAILS

Rapid Rails, also knows as "quick connect" rails, can be used with DELL racks as well as with other standard 19" four post cabinet racks with the standard square mounting holes. Rapid Rails use square, tab-style connectors to mount in the rack.

VERSA RAILS

Versa Rails are intended to be used with non Dell manufactured 19" four post cabinets. These cabinets use threaded, round holes and screws to mount the rails in the rack. VERSA RAILS may also be used with a DELL rack but they can not be snapped in and must instead be mounted using screws.

2-POST RAILS

The 2-Post Rail kits are used with standard telco racks that have 3" or 6" posts that employ screws for mounting. These rack kits cannot be used on four post racks.