| a single device group. All devices in a device group must be |
| on the same EMC Symmetrix unit. You can use a device group |
| to identify and work with a subset of the available EMC |
| Symmetrix devices. |
device streaming | A device is streaming if it can feed enough data to the medium |
| to keep it moving forward continuously. Otherwise, the tape |
| has to be stopped, the device waits for more data, reverses the |
| tape a little and resumes to write to the tape, and so on. In other |
| words, if the data rate written to the tape is less or equal the |
| data rate which can be delivered to the device by the computer |
| system, then the device is streaming. Streaming significantly |
| improves the performance of the device and use of space. |
DHCP server | A system running the Dynamic Host Configuration Protocol |
| (DHCP) providing dynamic IP address assignment and network |
| configuration for DHCP clients. |
differential backup | An incremental backup that backs up changes made since the |
| last full backup. To perform this type of backup, specify the Incr1 |
| backup type. |
| See also incremental backup. |
differential backup | (Microsoft SQL Server specific term) A database backup that |
| records only the data changes made to the database after the |
| last full database backup. |
| See also backup types. |
differential | A differential database backup records only those data changes |
database backup | made to the database after the last full database backup. |
direct backup | A |
| from disk to tape (or to other secondary storage) is facilitated |
| by the SCSI Extended Copy (Xcopy) command. Direct backup |
| lessens the backup I/O load on systems in a SAN environment. |
| The data movement is facilitated directly from disk to tape (or |
| to other secondary storage) by the SCSI Extended Copy (XCopy) |
| command. The command is provided by any element of the |
| infrastructure including bridges, switches, tape libraries, and |
| disk subsystems. |
| See also XCopy engine. |
358Glossary