Restore Operations4 DD400 Series Restorer User GuideTypical compression ratios are 20:1 over 20 weeks assuming weekly full and daily incrementalbackups. A backup that includes many duplicate or similar files (files copied several times withminor changes) benefits the most from compression.Depending on backup volume, size, retention period, and rate of change, the amount ofcompression can vary. The best compression happens with backup volume sizes of at least 10 MB.See “Display File System Space Utilization” on page 81 for details on displaying the amount ofuser data stored and the amount of space available.Global Compression functions within a single restorer. To take full advantage of multiple restorers,a site that has more than one restorer should consistently backup the same client system or set ofdata to the same restorer. For example, if a full backup of all sales data goes to restorerA, theincremental backups and future full backups for sales data should also go to restorerA.Restore OperationsWith disk backup through the restorer, incremental backups are always reliable and access time forfiles is measured in milliseconds. Furthermore, with a restorer, you can perform full backups morefrequently without the penalty of storing redundant data. With tape backups, a restore operationmay rely on multiple tapes holding incremental backups. Unfortunately, the more incrementalbackups a site has on multiple tapes, the more time-consuming and risky the restore process. Onebad tape can kill the restore.From a restorer, file restores go quickly and create little contention with backup or other restoreoperations. Unlike tape drives, multiple processes can access a restorer simultaneously. A restorerallows your site to offer safe, user-driven, single-file restore operations.ReplicatorThe Data Domain OS Replicator product sets up and manages the replication of backup databetween two restorers. After replication is started, the originator automatically sends any newbackup data to the replica.A Replicator pair is an originator restorer that receives data from backup servers and a replicarestorer that receives data only from the originator. You can mount the replica as read-only forrestoring data through systems other than the originator. A replica can also take the place of anon-functioning originator in a disaster recovery situation.Restorer Hardware InterfacesYou can configure and administer a restorer using a directly-connected serial console, an Ethernetconnection from another system, or a monitor and keyboard. All hardware interfaces are on theback panel of the restorer. See Figure 5 on page 12 and Figure 7 on page 14 for interface locations.
