Backup Restore Time Estimator

Estimating a backup window is a bandwidth division problem wrapped in unit conversions that are easy to get wrong. Network speeds are quoted in bits per second while data is measured in bytes, so 1 Gbps is 125 MB/s at the wire and about 450 GB per hour before overhead; TCP, framing and protocol chatter typically remove another 5 to 10 percent. Compression shrinks the numerator rather than raising the speed: at a 50 percent ratio, 2 TB of source data moves as 1 TB. Ratios are highly data-dependent - relational database dumps and log files commonly compress 60 to 80 percent, office documents 50 to 70 percent, compiled binaries 30 to 50 percent, and already-compressed JPEG, MP4 and ZIP content essentially not at all - so applying a blanket ratio to a mixed dataset overstates the saving. The governing constraint is always the slowest element in the path. A spinning disk sustains roughly 150 to 250 MB/s sequentially, a SATA III solid state drive about 550 MB/s, and an NVMe Gen4 device several gigabytes per second, so a 10 Gbps link is wasted behind a single hard drive. An overhead allowance of 10 to 20 percent covers catalog updates, checksum verification and snapshot management, and restores usually run 10 to 30 percent slower than the matching backup because they are write-heavy and must rebuild directory structure, permissions and database indexes. These figures feed the recovery time objective, the maximum outage a business will accept, which is a separate quantity from the recovery point objective describing tolerable data loss.

Backup timing has been a scheduling constraint since commercial computing began. The UNISERVO drive shipped with the UNIVAC I in 1951 as the first commercial magnetic tape storage, and IBM followed with the 726 in 1952. Because tape is a sequential medium, the whole discipline of overnight batch windows and generational rotation - the grandfather, father and son scheme - grew up around how long a full pass took. Capacity kept outrunning throughput, which is why the estimate matters. The Linear Tape-Open consortium was formed in 1997 by Hewlett-Packard, IBM and Seagate, and LTO-1 cartridges shipped in 2000 holding 100 GB; by LTO-9 in 2021 native capacity had reached 18 TB, far faster growth than the transfer rates available to fill them. Disk-to-disk backup and inline deduplication, commercialized by Data Domain from 2001, attacked the problem from the other side by not moving redundant blocks at all. Amazon S3 opened in 2006 and pushed backups offsite, but wide-area bandwidth became the new bottleneck - AWS introduced the physical Snowball appliance in 2015 precisely because shipping disks beats transferring petabytes over a network. The recovery time and recovery point objectives these estimates feed were formalized through business continuity practice and now appear in standards such as ISO 22301, while the widely cited 3-2-1 rule of three copies on two media with one offsite was popularized by photographer Peter Krogh in his 2005 book on digital asset management.