DPT RAIDStation and ServerOnCall
Need the ultimate in data protection? Don’t want to lose a byte, and get a lot of performance increase as well? Got lots of cash? DPT’s RAIDStation and ServerOnCall software are just your ticket.
DPT is well known for their excellent caching and RAID SCSI disk controllers. DPT has combined that technology with a stand-alone RAID tower and special server software to create a combination that ensures you will have high availability for your system’s data. The systems comprises a dedicated RAID tower (the RAIDStation) attached to one or two machines using DPT’s SmartRAID IV SCSI controllers. Dedicated ServerOnCall software controls the entire system. The result? Lots of disk storage, super-fast access, and reliability in case of not just a single disk failure, but a catastrophic failure of one server.
The RAIDStation 7 is a dedicated external case with nine slots in the front. The black case is tall, thin, and deep, matching most servers (except for the color), or it can be rack-mounted. Seven of the nine bays in the front accept special trays that contain SCSI drives. The remaining two bays accept power supplies (redundant, of course). For those who need more disk space, DPT also offers the RAIDstation 14, which as the name suggests accepts 14 disk drives.) The back of the RAIDStation has SCSI-II connectors to run to one or two controllers. A bank of DIPS allows you to set SCSI IDs for the entire RAIDStation.
Our review RAIDStation 7 was equipped with seven 4.3GB drives preconfigured as a RAID 5 array. This resulted in 29GB of storage. Using larger drives, you can configure up to 63GB (with 9.1GB drives) or more as high-capacity SCSI drives become available. The RAIDStation is intended to accept SCA (Single Connector Attachment) drives, which incorporate SCSI and power connectors in a single plug-in card. Non-SCA drives can be used, although SCA drives are the best bet.
Each drive is mounted in a special tray which has status lights and an eject button on the front. Don’t assume ejecting drives is simple: we had a heck of a time getting drives out of the RAIDStation, eventually having to disassemble the back panel to release the latch that hooks the drive to the steel case. The button on the front of the tray is supposed to handle this task, but didn’t work on any of our trays. Two LEDs on the tray show when the drive is active and when a fault has occurred. The power supplies (we had two for redundancy) slide into the bottom of the RAIDStation. The power supplies are hot-swapable. As with the drive trays, LEDs on the front panel show conditions of each supply.
Positioning the RAIDStation may be a problem for some systems. There must be a good supply of air around the case. DPT recommends at least a meter (3 feet) between the back of the case and a wall or partition. We did manage quite well with less, but you can’t stick the RAIDStation in enclosed areas without auxiliary fans. Also, since there is the equivalent of two meters of SCSI cable internal to the RAIDStation, you must be careful about total SCSI chain lengths. We used two five foot cables with no problems. Using Differential SCSI you can get away with lengths up to twenty-five feet.
Setting up the RAIDStation took about half an hour, including installing the SmartRAID IV cards in two servers. (You could install one card in one server, or two cards in two different servers, depending on your needs. You can also expand from one card to two at any time.) Our SCA drives were premounted. If we had to do the mounting ourselves, another couple of hours would be required.
After installing the SmartRAID IV cards and connecting the RAIDStation, the ServerOnCall software comes into play. You can install the SCO version of ServerOnCall when loading the operating system or add it to an existing server. ServerOnCall uses a BTLD (Boot Time Loadable Driver) to handle the RAIDStation. ServerOnCall also runs with Windows NT 4 and Novell NetWare. We tested it with both SCO OpenServer 5 and Windows NT 4 Server. Those who run DPT cards with their Storage Manager software have to uninstall Storage Manager and load ServerOnCall fresh. Installing the software is quick and painless.
ServerOnCall can monitor three servers at once through add-on cards to the SmartRAID single-chain unit. In a double server configuration with the RAIDStation, up to six machines can be monitored at a time, if you want to go that far. We set up our system to monitor two servers only (the two machines connected to the RAIDStation). When ServerOnCall detects a problem with a monitored machine, a failover process begins that forces a reboot of the unresponsive server.
As supplied to us, the entire subsystem (two SmartRAID IV cards with 4MB cache each), ServerOnCall for SCO OpenServer, and RAIDStation with two power supplies and seven 4.3GB drives) costs about $12,000 all together. While that’s not much compared with some of the high-priced multi-processor servers available today, it’s still a heck of a lot of cash. What do you get for that investment? Quite simply a system that’s almost impossible to fail. We yanked drives, yanked one of the two power supplies, and disconnected a cable between one server and the RAIDStation and the system kept right on delivering service. When one server was forced to die, the other took up the load and ran just fine. With a failed drive and a replacement hot-swapped in, the system reformatted and copied data to the new drive transparently, bringing it on-line when ready. The only way to crash the RAIDStation is to disconnect the two SCSI cables, kill both servers, or power down the entire RAIDStation. Not a likely occurrence for most setups, which means this is data available all the time, every time.
We loaded our Web server system on the RAIDStation, along with the complete OpenServer software, and measured performance compared to a standard 4.3GB SCSI drive attached to the same SmartRAID IV controller. Because of RAID 5’s parallel read abilities, data reads from the RAIDStation were about three times as fast as from the stand-alone machine. Writes were a little faster, but not measurably so, which is expected for RAID 5. When we had two servers handling the RAIDStation, failing one let the other continue handling all Web requests without a client knowing there was any difference.
There’s a simple bottom line here. The ServerOnCall and RAIDStation setup is the best way we’ve found to guarantee high-availability data and server behavior. It’s expensive, but it’s always there. Since drive prices are always dropping and the system can be set up in a step-by-step expansion process, adding drives and redundant controllers as funds allow, it’s also not that expensive to get started with RAIDStation. Highly recommended insurance for your system.