The fine print

When paying a storage service provider to buy and maintain storage equipment

for you, the service-level agreement is the contract that spells out the

terms and conditions of the services you will receive. This, of course,

determines the price you will pay. The agreement also states how you will

be compensated if the service provider fails to deliver as promised. The

typical remedy is a deduction in the monthly service fee.

Here are some of the key terms in a service-level agreement:

* Availability. Storage system availability requirements usually start

at about 99.9 percent of the time. Adding more nines to the right of the

decimal point increases the service's cost, but for certain critical applications,

it is well worth it.

* Frequency of backups. Typical schedules involve full dataset backups

once a week and incremental backups daily of data that has changed. More

frequent backups cost more money.

* Data mirroring. The ultimate in data backup is to create two copies

of all data; it's also the most expensive because it requires twice as much

storage capacity.