Making Sense of SBS Storage (Advanced Windows Small Business Server 2003 Best Practices)

Hiya – I am the publisher of the Advanced Windows Small Business Server 2003 Best Practices book – and I like to hold vitual book readings from time-to-time. So here is a passage on Storage! BTW – I would be remiss if I didn’t mention that my SBS 2008 book is now here! cheers…harrybbbb

Making Sense of the Storage Scene

If you look at a hierarchy of storage performance, at the top you’ll see the ultra- fast temporary registers that are within all processors, several levels of temporary cache, then system memory, and then persistent storage—hard drives—at the very bottom. While hard drives are the slowest data repositories in the storage chain of command, they also offer the most value per megabyte (or more commonly, gigabyte) of capacity, and several new and upcoming technologies promise to alleviate some of bottlenecks that hard drives traditionally impose.

One reason that hard drives are so slow is that, unlike cache or system RAM which are strictly electrical components, magnetic drives are mechanical in nature, using moving parts that need to operate with utmost precision. Moreover, the basic drive operation has gone more or less unchanged for years: the drive receives read and write requests from the chipset, the requests are sent to the drive’s onboard buffer, and they are then executed by the drive’s controller. But changes are now being made, both inside and outside of hard drives themselves, to improve both performance and flexibility alike.

Serial ATA

Serial ATA is a connecting technology that facilitates communication between chipsets and storage devices such as hard drives and optical drives. It’s characterized by a four-wire interface cable—miniscule by comparison with the unwieldy 80-conductor IDE cables of yesteryear. Consequently, it’s much easier to route cables and maximize airflow in systems with multiple Serial ATA hard drives.

Beyond the appeal of its physical implementation, Serial ATA facilitates faster data transfer (up to 150 MB per second), even if today’s hard drives aren’t able to keep pace with the interface itself. More important, Serial ATA maintains backward compatibility with parallel ATA drives, so you can make the transition on your workstations and low-end server without worrying about interoperability.


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The second generation of Serial ATA promises more features for the server market. The interface will begin by offering 3 Gbps of throughput, or a maximum of 300 MB per second. Performance is further improved with the implementation of Native Command Queuing (NCQ), a technology that facilitates the reordering of commands for organization in the most efficient manner, most effective in non-sequential transfers. Hot-plug support is planned as well.

With so many new enterprise-level features trickling down to mainstream drives, it’s immediately tempting to tap Serial ATA for use in servers. Just keep in mind that Serial ATA is still intended for desktop use, where duty cycles hover around eight hours a day, five days a week. Serial ATA drives don’t tolerate rotational vibration well, they transmit in half-duplex mode (meaning that data can only move in one direction at a time), and they don’t include the same internal data integrity checks as those built into the SCSI and SAS devices I discuss next.

Serial ATA in an SBS environment carries with it the benefit of reduced cost, high performance in ideal conditions, and excellent reliability in the context of a RAID 5 disk array. However, it does bear a few caveats, mainly that Serial ATA drives aren’t as reliable as SCSI, error-recovery occurs at the controller level rather than the drive level, and the addition of hot-spares adds to cost. Bottom line, though— if you’re looking to save some money on storage, Serial ATA is a phenomenal alternative to costlier SCSI arrays, for a smaller SBS server.

SCSI and Serial Attached SCSI (SAS)

SCSI dates back to 1986, when it materialized as an 8-bit bus running at 5 MHz. Since then it has slowly matured up to 320 MHz, amplifying issues with its parallel bus that transfers multiple streams of data concurrently. However, attenuation, signal reflections, and cross-talk now prevent further evolution of parallel SCSI technology. So naturally the door is open for Serial Attached SCSI (SAS), another serial technology that is more attuned to the needs of enterprise customers than is Serial ATA. Figure 2-4 illustrates the improved connecting mechanisms of Serial ATA and SAS.

 

 

Notes:


CHAPTER Chaper 2 1 So Understanding You Want to Hardwre Be an in SMB the SBS Consultant?!?! Environment

Figure 2-4

Keying between the power and data ports differentiates Serial ATA and Serial Attached SCSI (SAS). Image courtesy of Maxtor.

SAS takes over where Serial ATA left off by adding full duplex communication, a dual-port interface, and maximum cable lengths of 10 meters. As you can see in Figure 2-4, the connectors for Serial ATA and SAS are very similar, the latter featuring a filled keyway to prevent an SAS drive from plugging in to a Serial ATA interface. The second port sits on the opposite end of the drive, for access to the drive from two independent sources. SAS supports expansion through edge expanders, which accommodate up to 64 SAS or SATA ports, though you almost certainly won’t need to worry about that degree of expansion even if you do dabble with SAS at some point.

In addition to the robust expandability of SAS, SAS drives are able to offer greater reliability and performance than their Serial ATA counterparts. Serial ATA maintains respectable throughput in environments without rotational vibration, but drops off quickly when confronted with the subtle vibrations associated with random actuator movement from nearby drives. SAS, on the other hand, is largely immune to reasonable levels of rotational vibration. And while the newest Serial ATA drives are blessed with 1,000,000 MTBF ratings, SAS drives sport even higher ratings under more grueling duty cycles.

Hard drive manufacturer Maxtor recently illustrated the flexibility of both SAS
and Serial ATA by demonstrating the two technologies working together in a


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three terabyte array with an LSI Logic host bus adapter (HBA) and Vitesse expander. In a recent discussion with representatives who oversaw the demonstration, I confirmed that SAS will work natively with Windows Server 2003, and thus with SBS.

Network Attached Storage (NAS)

An increasingly popular storage medium that doesn’t tax your SBS server or its clients is the Network Attached Storage (NAS) device. Think of an NAS device as a dedicated file server, only instead of employing general-purpose hardware, it uses highly integrated, embedded subsystems to minimize cost, maximize reliability, and perform its duty of delivering data to clients as efficiently as possible.

NAS systems operate independently of your SBS machine and are accessed over the network, just like any other client with shared resources. But because they are specialized, NAS devices generally cost less than configuring a separate server, and are often more scalable as well. The resulting benefits include simplified management, cross-platform data-sharing, and reduced load on your primary server.

NAS is particularly attractive to SMBs with moderate file-sharing requirements and enough network bandwidth to make centralized storage feasible. On the other hand, if you don’t work with a lot of collaborative information, an NAS appliance might be unnecessary.

 

 

BEST PRACTICE: Be sure to check Microsoft’s Windows Server Catalog at www.microsoft.com/windows/catalog/server/ to verify that Windows Server 2003 supports the device that you’re eying.

Hard Drive Summary

When considering a hard drive purchase, once again you’re faced with a decision between cost and performance. Serial ATA has it benefits, as does SAS. Fortunately, both technologies, with all of their inherent benefits, should maintain price parity with the parallel interconnects they replace.

One area where you might notice a difference between Serial ATA and SAS is in the cost of controllers. Because Serial ATA is predominantly a desktop interface, most modern platforms include native support. And in an attempt to integrate the most compelling feature set, several vendors include RAID 0 and


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RAID 1 capabilities as part of the package. For example, Intel’s ICH6-R I/O controller features Matrix RAID technology, to turn two Serial ATA hard drives into separate RAID 0 and RAID 1 arrays by using a pair of partitions on each. It’s tricky stuff to be sure, but it emphasizes the value that chipset manufacturers are putting into their Serial ATA offerings. Expect to pay several hundred dollars extra for a server with SCSI capabilities and 10K- or 15K-RPM drives.

cheers….harrybbbb

Harry Brelsford, CEO at SMB Nation (www.smbnation.com)

MBA, MCSE, CNE, CLSE, CNP, MCP, MCT, SBSC (Microsoft Small Business Specialist)

PS – my Small Business Server 2008 (SBS 2008) book is now here!

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