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Disk Versus Tape

Tape Backup vs. Disk Backup - Pros & Cons

Moving to Disk-Based Backups

The high adoption of disk-based data protection solutions is a result of increasing data capacities and the unique ability of disk-based data protection solutions to meet backup windows that cannot be met with tape. The needs of businesses small and large have outpaced the capabilities of tape backup technologies in recent years.

Customers evaluating alternatives to tape will be faced with three basic options:

  1. a new tape backup solution
  2. a mix of disk and tape (disk-to-disk-to-tape) that uses disk as a staging space before data migrates to tape
  3. a fully disk-based alternative (disk-to-disk-to-disk)

A quick summary of the differences is shown in the following table:

Tape-based Backup Disk-to-Disk-to-Tape Disk-to-Disk-to-Disk
Scaling Data Poor Better Best
Scaling Performance Poor Better when accessing recent data, but poor for long term data Best - disk is random access, and RAID allows for higher throughput
Reliability Poor – tape stretches and suffers magnetic damage Poor – same issues with tape Good – disk drives and RAID make disk backups much more reliable
Security Poor tape reliability, lost or stolen tapes Better Best
Usability Poor – managing tapes is one of the biggest issues IT managers face Poor – doesn’t eliminate the issues with tape, and introduces multiple components Easier to manage and maintain
RPO Okay, but requires more full backups and more storage Better for data still on disk, but requires more full backups and more storage Great with more incremental backups
RTO Poor Better for recent data Great for all data
Backup Window Lengthy Shorter Shorter
Removability for Offsite Vaulting Good Good Good with Eversync archiving to removable drives
Cost Savings Due to Capacity Reduction None – limited deduplication and requires more full backups Higher savings due to deduplication and less frequent need for full backups Higher savings due to deduplication and less frequent need for full backups
Cost High High – complexity and licensing of multiple components, often from different vendors Lower when using an integrated appliance
Long Term Archiving Removable, but still a poor solution for long term data retention if you ever need to read the data Poor solution for long term data retention Capable of long term data retention

Major Advantages of Disk Technology Over Tape Technology

Faster Restores

The random access nature of disk drives enables the instant merging of incremental backups. Contrast this with tape, where multiple incremental backups are often spread across multiple tapes and likely to be far from the start of the tape. The RAID configuration of the disks in a backup appliance allows for redundancy and increased throughput by backing up and restoring multiple clients simultaneously. So when you need to restore a file, or even a single email, you can find it and restore it in a matter of minutes without sorting through any number of tapes.

Shorter Backup Windows

Disk-based backups reduce the backup windows in two ways. First, random access and higher reliability of the disk media means you can leverage more incremental backups per full backup. Full backups can be scheduled much less frequently, or selected to coincide with an expected lull in operations (for example, over the weekend). Since incremental backups typically need to save a small fraction of the total data, most backup windows become much shorter. Second, multiple clients can be backed up simultaneously with disk-based backup which results in higher throughput.

Economies of Incremental Backup

Leveraging more incremental backups not only helps with performance, but also with cost. Due to the additional time penalties of incremental tape restores and because tape restores frequently fail, almost all IT shops keep many copies of full (Level 0) backups in their tape libraries. Most tape backup schedules use no incremental backups or only a small number for each full backup set. That means there are often many redundant copies of the same file on tape. This significantly increases the $/TB of the tape media by wasting capacity on unnecessary duplicated file storage.

Accelerated Backup and Archiving

Another benefit of disk-based backups is performance. Disk-based solutions leverage RAID performance and reliability to quickly back up and restore data.

Greater Reliability

Research has found that as many as 70% of tape recovery attempts fail. Disk-based solutions benefit from very reliable commodity disks, made even more reliable by using RAID to protect against disk failures. There are no tapes to misplace, or robotics to jam and recalibrate. Disk drives are self-contained and less sensitive to environmental conditions, so they can be reliably used for a longer period of time in more diverse environments. For most SATA drives, the manufacturer’s warranty is 5 years.

Easier Management

Disk-based solutions are easier to manage overall. The interfaces and concepts of file system, disk, and network attached storage (NAS) are familiar even to entry-level IT staff, meaning less training and fewer mistakes from the start.

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