Tape Drives - Notes 1

This article (not in its entirety) was taken from http://www.mactech.com

Backup Management

by Paul Shields

A guide to managing local and remote backups for your Mac

When was the last time you lost data because of a hard drive failure? How about by accidentally deleting a file, whose name you did not recognize or felt you no longer needed? Have you ever lost data because of a fire or theft? All of these represent real situations that people face every day. How long before you encounter a similar situation?

Backups are one of the most critical, but often neglected, tasks in proper data management. Both home users and network administrators have lax attitudes towards backups until the day comes when they lose data, especially important business-related data. With the refinements in hardware and software technologies backups are easy and relatively inexpensive, even for the small office and home users.

How effective is a company where the list of customers is lost because of malicious activity by a former employee or Internet hacker? Can a company survive if its financial system lies in ruins because a hardware failure rendered it useless? As systems administrators your responsibility is to protect corporate computing assets. Since data is becoming one of the most valuable assets a company has, implementing a reliable backup system is essential. As a business owner, you must take interest in the processes used to protect your assets. There is no excuse for being caught off-guard.

Before beginning a discussion on implementing a backup system, we must define some of the common terms.

Full backup

A full backup is a complete copy of everything on the source drive to the backup media. Most users and administrators run a full backup on a weekly or monthly basis.

Incremental backup

An incremental backup only copies the data that has changed since the last backup. Administrators will run incremental backups on a daily basis to capture the data files added or updated during the day.

Differential backup

A differential backup copies the data that has changed since the last full backup. It is important to understand the difference between an incremental and differential backup. Administrators use differential backups to facilitate more complex tape rotation schemes and sometimes in database environments.

Archiving

Too many administrators fail to understand the difference between archives and backups. They fail to see the powerful capabilities of archiving and use their normal backups as archival storage. Archiving is the process of moving data from one media (typically a hard drive) to another media (optical disks or tapes). Archiving deletes the files from the original location. Companies may use archiving to store things such as historical financial data. Archiving saves space on hard drives, while retaining the ability to restore the data quickly.

Each media type has dramatically different characteristics including lifespan, storage capacity, re-usability, and costs. Even within a category such as tape drives the number and variety of options available is broad enough to suit a wide spectrum of users. One important factor in selecting a media is the length of time you plan to store the media. Table 1 provides a lifespan comparison of some of the most popular backup media.

A common mistake is to pick a media type based on the needs of today's systems. The data requirements of businesses are growing at a phenomenal rate estimated to be as high as 70% per year by the Gartner Group. A system that barely meets the capacity and performance requirements of your current systems will be inadequate within 18 months and the search will be on for a replacement. Switching media types is an expensive and time-consuming proposition.

Tape drives

Tape is the standard in the backup systems of the majority of corporations. Tape offers extremely high capacities, excellent performance characteristics, and a reasonable lifespan. The variety of formats makes tape a versatile media that can fit in a number of environments. Table 2 provides a summary of the most common tape types and their specifications.

For a home or small business user, the low cost of the Travan drives makes them an appealing option. The catch is the high media costs per GB and the slow performance. Although 60 MB/min sounds fast, a typical hard drive is now 4 - 8 GB, which translates into a full backup time of 1 - 2 hours. This long backup time makes it a nuisance and you are less likely to be anxious to give up access to your machine for a few hours while it backs up.

For a large organization, picking the right technology depends on the type of backups. Most administrators deploy DAT tape drives for network backups because they are less expensive and offer good performance and capacity. AIT and DLT offer more capacity and better performance but are expensive. DLT and AIT are perfect for situations where you attach the tape directly to a fileserver because of the large amounts of data on the server.

The reason DLT and AIT may not fit well in a typical network backup is the potentially slow performance of moving data between machines. The latest releases of Retrospect and OS 8.5 combined with a quality TCP/IP network can come close to the speeds needed to use the full capacity of a DLT or AIT system.

To find out why DAT may be better for network backups than DLT compare the difference in performance between a 10Base-T network and DLT drives. At best, a 10Base-T network can move data at about 1 MB/s. A DLT writes data at a minimum of 1.8 MB/sec. This gap is even wider with the new AIT II tapes and the proposed SuperDLT format. DAT drives more closely match the performance of a 10Base-T network and have a lower cost per MB. DLT is still viable and I use it for network backups on a regular basis, primarily because of its longer lifespan and better durability.

Another reason to choose tape as a backup media is the availability of tape libraries. A tape library is a device that contains one or more tape drives along with dozens or hundreds of tape slots. These systems have a robot that can automatically swap tapes as directed by the host computer. Tape libraries greatly enhance the storage capabilities of a backup server. No longer do administrators have to limit backups to what will fit on a single tape or constantly monitor the server and rotate tapes. The software automatically swaps tapes as they fill. Retrospect supports a number of tape library systems via the Advanced Driver Kit option.

Most tape drives have a SCSI interface, which poses a problem for iMac and B&W G3 owners without a SCSI card. Until Firewire or USB connections become more common on tape drives, users must consider alternatives or buy an adapter. USB is a low-speed interface and while adapters exist, the performance they offer will be disappointing. Firewire offers performance levels higher than traditional SCSI, so the use of an adapter should provide adequate performance. Tape drives with native Firewire should begin to appear in the next 6 - 12 months.

CD and DVD

Over the last few years, CD and DVD have become viable backup media for small businesses and critical data in large businesses. As shown in Table 2, both CD and DVD drives offer good storage capacity and performance with moderate media costs.

The real advantage of a CD or DVD is the long lifespan of the media. Optical media can last as long as 30 years before oxidation starts to affect the stored data. This makes optical media perfect for storing archives of critical data such as financials or personnel records.

One note of caution when considering DVD is that the capacity is 2.6 GB per side. Switching sides on the DVD recorder is a manual process, which interferes with scheduling unattended backups.

Removable drive technologies

Zip drives are almost universally available and are relatively inexpensive. Jaz drives offer more capacity and better performance while retaining a relatively low cost. These media though do not offer extremely high levels of reliability and are best suited for file transfer, occasional ad-hoc backups, and short-term storage.

Another problem with removable media is the high costs of media. A typical Jaz cartridge costs $90 and stores 1 GB of data. A typical hard drive now tends in the 6 GB range. If we assume the hard drive is full and that you run a full backup once per week, then the yearly cost approaches $28,000. While you may be able to reduce this cost slightly by recycling cartridges, these costs do not account for having duplicates of your backup media (highly recommended) nor the media used for daily incremental backups. This compares poorly to DAT, which under the same conditions has a yearly cost of just over $1000.

One promising technology is the Orb drive from CastleWood http://www.castlewood.com/. The Orb uses traditional hard drive media and offers the potential for improved reliability as compared to the Zip/Jaz technologies. EIDE versions are shipping now, while SCSI, USB, and Firewire version should be available by the middle of the year. The Orb solves some of the media cost problem by reducing media costs to approximately one-third the cost of Jaz media. While this difference does not make the Orb a competitor to tape in most situations, it may make it acceptable in some circumstances.

Which one is right for your needs?

Most users should avoid removable magnetic drives because of their limited capacity and short lifespans. A small business with a few machines could probably do well with the older DAT technologies (DDS-2 or DDS-3). Both offer good performance and low media costs. The newer DDS-4 drives also support the older tapes, so when it comes time to upgrade there is an evolutionary path.

If you needs are beyond the capacity of DAT, both DLT and AIT are excellent solutions. DLT has been in the market place longer and is potentially a more stable technology. Sony is pushing the AIT standards hard though and the recent AIT II drives surpass DLT in performance, capacity, and media costs. A network administrator will not go wrong with either of these technologies, especially for backups of large data servers.

Where to put your backup tapes?

Few administrators take the appropriate actions when it comes to storing their backup tapes. All too often when you ask the systems administrator where the backup tapes are, they point to a cabinet in their office. This is strictly a matter of convenience and complacency. Administrators hesitate to send the tapes off-site because as soon as they do, a user will request a file restore and they must bring the tapes back on-site. The complacency is because so few network administrators have been through a major disaster that resulted in a major loss. Few companies have a disaster recovery plan they enforce and there is little incentive for the network administrator to create one.

Home users and small business should invest in a fireproof safe at a minimum. A better solution is to find a secure off-site storage location like a safe deposit box at a local bank. Either way, the data is safe from the most common hazards such as fire, theft, or other unfavorable environmental conditions.

For large organizations, storing the tapes at a remote office or an off-site storage company is ideal. When selecting a site, ensure that the provider maintains proper environmental conditions and takes measures to control access to the backup media. Our local off-site storage company will not reveal its exact location under normal circumstance. They provide a courier pick-up and drop-off service for transporting the tapes between sites. We ship the tapes in sealed boxes to ensure that no one tampers with the contents.

Once you select a storage location, its time to decide how often the media will rotate off-site.

Developing a rotation schedule

The media rotation schedule forms the basis of your backup schedule. Its at this point that you start asking questions like, how much data can I afford to lose? There is no set standard for defining a schedule but there are a few guidelines. The exact schedule you choose will depend on the amount of backup data and the critical nature of the data.

The most common method is to do one full backup per week, usually over a weekend, and incremental backups the rest of the week. You have the option of placing the full and incremental backups on separate tapes, allowing you to ship the full backups off-site immediately on Monday morning. The incremental backups from the rest of the week are on a second set of media. You then ship the incremental tapes off-site on Friday before the next full backup. This gets the media off-site quickly and minimizes the amount of data at risk.

The problem with such an aggressive off-site storage policy is the inevitable restore request. The administrator must pull tapes back on-site to complete the restores. A potential solution is to bring the older backup tapes back on-site which may cover some restore requests and minimize the amount of tape shuffling.

Another option is to duplicate tapes before sending them off-site. While this method does double your media costs, it allows you to have one copy off-site for disaster recovery and one on-site for restores. To duplicate backup media you will need a machines with two drives. Retrospect has a feature to facilitate duplication of media.

The important thing is to keep the tapes off-site as much as possible. The whole purpose of backups is to provide safe and secure storage for critical data. Leaving them on-site means they are vulnerable to the same disasters that may destroy the original source.