HARDWARE: Consolidation
The idea of server farms seems to work against recent trends to server consolidation (replacing multiple distributed servers with a smaller number of more powerful models to gain economies of scale and reduce management costs).
According to McIsaac, this works well when you consolidate multiple homogenous servers running a single application such as Exchange, Notes, or file and print services.
Twenty old machines can be replaced by perhaps five new ones due to the increased power of more recent hardware. It's harder to gain the benefits if you try to consolidate multiple applications or multiple databases onto one server.
McIsaac says he recently saw a quotation offering the customer a choice between two large servers or 12 smaller ones, with the former costing AU$5 million more. Given the total cost of employing highly skilled staff and a generous five-year useful life for the hardware, he suggests the customer would need to cut five staff to compensate for the increased hardware cost. "I don't see five people--worth of savings--you might save half a person," he says.
HARDWARE: Storage
Consolidation is paying off in the storage market. "There is more external storage being sold than internal," says Abie Gelbart, product manager at EMC. "People are realising storage needs to be separated from the server."
The main advantage of this arrangement is that it simplifies storage management. Instead of making the various system administrators worry about storage, responsibility can be transferred to one team that can look after all the storage resources with a single piece of management software.
But if you're going to put all your eggs in one basket, "you need to make sure that basket is very strong," says Gelbart. External storage units--such as those from EMC--can be designed so any single component can fail and be replaced while all data remains available.
For example, disk drives are usually configured as RAID pairs. If one drive fails, data is automatically copied from the surviving member of the pair to a spare drive.
In practice, it may not be necessary to read the data from disk at all, as such units are equipped with large memory caches. In any case, the copying is done as a background process and need not have any impact on performance.
High availability also requires redundancy in the SAN so there are at least two paths from the storage unit to each of the servers it supports.
"We try to focus on 100 percent 24 x 7 availability," says Gelbart. Scheduled downtime accounts for 85-90 percent of outages, he says, and while the storage units can be repaired or upgraded on the fly, events such as building work that requires the power to be disconnected or the air conditioning shut down can force downtime. "There are devices out there that have been up continuously for over a year," he says.
While mirroring can ensure the availability of files, backups are still important to protect against software failures that write incorrect data into the files, says Gelbart. Frequent backups will reduce the recovery time if this should occur.
Disk-to-disk backups are becoming more popular due to a speed advantage over tape, he adds. Remote copies of a database can be split from the main system according to a backup schedule, and then used to restore the data when necessary.
Even a low-end server benefits from using external hard drives. If the system fails, a relatively unskilled person can swap in a spare machine and reconnect the drives.
This can be especially useful for branch offices that are too small to justify on-site support staff.
Separating processing from storage can be advantageous even when the application seems bound up with storage. For example, mail servers such as Exchange and Notes can be called upon to handle huge amounts of data, and asking users to handle archiving for themselves is inefficient in terms of storage costs and person-hours.
StorageTek's Email Xcelerator suite moves messages and attachments into a separate database, replacing the originals with pointers to the new copies. The Exchange or Notes database is therefore much smaller, so backup and restore times are improved. According to Michael Palermo, director of StorageTek's ASM business group, restoring the pointers to a 10T database of messages and attachments can be done in a matter of minutes.
The external database is managed by StorageTek's Application Storage Manager (ASM), which can spread data across multiple storage units for reliability and across a storage hierarchy (eg, all messages might stay on disk for 45 days, then on high-performance tape for a year before being transferred to archive tape for seven years).
So "what is it that you need to back up and restore?" asked Palermo. Even if the original Email Xcelerator database has been destroyed, the restored Exchange or Notes database will reconnect to the additional copies created by ASM.
Network attached storage is sometimes used as a quick and easy way of providing workgroups or applications with extra storage without having to reconfigure the server.
Where SANs address the needs of large databases and moving blocks of data around, NAS focuses on sharing. One way of ensuring the availability of data stored on NAS is to use NAS servers that do not contain their own disk drives but instead connect to a SAN in order to access enterprise-class storage units.
This simplifies the storage environment and therefore makes it more manageable. Data availability is further improved by clustering these NAS servers with a spare unit to provide automatic failover, Gelbart explains.
