PCI card products are the least-expensive SSDs; pricing for Platypus Technology's QikDRIVE8 starts at $1470 for 1GB of SDRAM, and CENATEK's RocketDrive Solid State Disk starts at $999 for 512MB of SDRAM. These two products provide external power supplies that protect data when you power down your computer, but they don't provide redundant power sources to protect data during a power outage or a failure of the cards' external power adapters while the computer is shut down. The UPS that keeps your servers alive can also maintain data in the SSD, but unless the UPS software can copy data from the card to a hard disk before the UPS battery dies, you could lose data if an extended power outage occurs after business hours. Losing data might not be a concern when you use the SSD to improve access to a terminal server's swap file, but you probably don't want to use these types of SSDs for files that contain critical data. At press time, CENATEK said it will soon introduce a new product called RocketDrive XL that will incorporate a battery, automatic backup software, and a hard disk. CENATEK hasn't set pricing for the product.
Most of the more expensive SSD products provide built-in UPSs and hard disks to protect data. If power fails, batteries maintain the data while the system copies it to the SSD's hard disks. Imperial Technology's MegaRam-35 provides this technology; its disk, memory, battery, and Ultra Wide SCSI interface components fit into a 3.5" disk bay. This added protection increases the product's price, however; a 1GB internal configuration sells for about $10,000. The MegaRam-35, which supports up to 4GB of SDRAM, is also available in an external configuration. Surprisingly, this high-speed product (which is relatively expensive) is equipped with a 40MBps SCSI Ultra Wide interface rather than an Ultra160 SCSI or Fibre Channel interface. But even with that interface, Imperial claims the MegaRam-35 can perform close to 10,000 I/O operations per second by using a 4KB frame size—much faster throughput than you'd expect from a large array of rotating disks.
Platypus's QikDATA provides similar features in a 1U (1.75") rack-mount chassis that holds 2GB to 16GB of SDRAM, a UPS, and two mirrored hard disks that receive the SDRAM's stored information when power fails. QikDATA connects to a workstation or server through the vendor's proprietary 64-bit 66MHz PCI interface card. Platypus says its proprietary interface delivers all the bandwidth your PCI bus can handle; with a 64-bit PCI slot, this is substantially more bandwidth than an Ultra160 SCSI interface can deliver. A QikDATA SSD configured with 2GB of SDRAM sells for about $20,410.
BiTMICRO Networks takes a different approach with its E-Disk, which, like MegaRam-35, fits into a 3.5" disk bay. The E-Disk uses only a small amount of SDRAM as a cache; its primary storage medium is flash memory, which doesn't require power to maintain stored information. During a power failure, the E-Disk's small battery refreshes the SDRAM while it copies stored data to as much as 77GB of flash memory. Although flash memory's ability to store data without power is a benefit in an SSD, flash memory also has potential limitations: Its typical life span of 100,000 to 300,000 erase/write cycles makes it inappropriate for enterprise-level transaction-processing applications. However, BiTMICRO claims to have overcome this limitation (for the company's explanation, see http://www.bitmicro.com/BiTMICRO_E-Disk_Features.pdf). You can purchase the E-Disk with SCSI Narrow, SCSI Ultra Wide, or Fiber Channel interfaces. E-Disk with 1GB of flash memory and a SCSI Ultra Wide interface costs about $1750.
Sharing SSD
The products I discuss in this article connect directly to a workstation or server, but you can share some SSDs—either through direct connections to your servers or through a SAN—to improve the performance of applications that run on several servers. Texas Memory Systems, Imperial, BitMICRO, and other vendors offer products you can use in a SAN environment. These vendors say they've tested their products with several Fibre Channel switch fabrics and host bus adapters (HBAs), but you'll need to contact them to confirm compatibility with your specific configuration.
As with the directly attached MegaRam-35 and QikDATA SSDs, shared-SSD products typically provide built-in batteries and hard disks to protect data, but they also include redundant batteries or power supplies as well as fans to ensure reliability. These 19"-wide rack-mount units also let systems administrators monitor system performance, perform diagnostics, and check battery and fan status and power-supply temperature from a remote location.
In addition to these features, Texas Memory Systems' RamSan-210 can write data to SDRAM and both of its internal disk drives in realtime; it reads data only from SDRAM. The RamSan-210 supports 8GB to 32GB of SDRAM in its 2U (3.5") chassis (an 8GB configuration starts at about $36,000) and features four Fibre Channel ports you can connect to several Fibre Channel switches for redundancy. For companies that have Network Attached Storage (NAS) systems but haven't implemented SANs, Texas Memory Systems offers a similar model, the NAS-250, that it markets as a storage accelerator for NAS systems. You can purchase the NAS-250 with two Gigabit Ethernet ports, and it supports Server Message Block (SMB) and NFS file systems so that you can access it from Windows and UNIX clients. Prices for NAS-250 start at $39,000 for 8GB of SDRAM and one Gigabit Ethernet adapter.
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