What's the difference between backup and archiving? And what are the pros and cons of the three most common media--tape, disk, and optical? We set a budget of AU$20,000 and asked three vendors to come up with a storage solution.
The amount of data that organisations are storing is increasing quite rapidly.
There are a few factors that are contributing to this growth. There are many industries that are legally bound to preserve large amounts of data for years, such as health care, financial services, and government. There's also widespread use of enterprise applications such as customer relationship management (CRM), enterprise resource planning (ERP), and supply chain management (SCM) that also increase storage needs. And of course, there's the explosion of e-mail, which companies also need to hang on to for a long time.
A recent survey carried out by InfoStor found that companies intend to purchase more tape and more disk storage. The survey also found that speed, capacity, and reliability were the main factors concerning those who make purchasing decisions.
There are many different strategies for archiving data, which brings on the debate about which archiving medium fits your needs the best.
Tape, Disk, or Optical
Sometimes picking the right solution to best meet your business needs may mean having a combination of these technologies, which would ensure your covering all your bases.
See the table below for a brief summary of the advantages and disadvantages of the various storage media.
| Medium | Advantages | Disadvantages |
| Disk |
|
|
| Tape |
|
|
| Optical |
|
|
Backup or archive?
Some people are not clear on the difference between backing up data and archiving. So before considering any of the technologies you should decide whether you need an archiving or a backup solution. Having a better picture of what the differences are will help you develop the best storage solution.
When it comes to backing up data all you are doing is creating an exact mirrored copy of your company's data. This data is rarely restored and is simply a reserve in case something happens to the original data. Backing up data isn't costly and has typically been done using tape devices. The only problem here with tape is when you do have to restore certain data it may be difficult and time consuming.
If you're going to be accessing your data over and over again you should be archiving your data. You can do this by logically placing data where it can be easily retrieved. That's the main difference but many companies still are confused about backing up and archiving. Many just think as long as they have a copy of the original data somewhere it will be fine.
It can prove very costly to store data on network drives. You don't want to be using up valuable storage space on your network with infrequently accessed data and if by chance the network isn't accessible, you could find yourself in all sorts of trouble.
On the other hand, if you were to use a recent tape backup to restore data you may find most of your staff will not have the patience or the technical know-how to find specific data from the tape.
A simple concept called hierarchical storage management (HSM) was developed to provide the ability to define and automate intelligent, cost-effective decisions regarding where and when data is stored. The notion was based on the fact that not all data is equally useful. Some may be required immediately, but with less frequently accessed data, slower transfer rates are much more tolerable as well as less expensive.
One of the main advantages of archiving is that it gives companies greater control over their data. For a large organisation, archive management software could enable them to operate a departmental storage system. Each department can then be given a specified amount of storage to archive data.
Where an organisation has many sites, archiving software can be embedded within the company's intranet to make storage and retrieval simple and consistent across the organisation.
Then there are optical discs. We found that using optical libraries and archiving software can simplify the process of storing data and retrieving it later. Using optical discs are the best choice for companies that need to store data which cannot be erased. DVD-R discs can hold 4.7GB of data and the library system that automate the loading of the discs mean that the storage capacity of the archive system can grow alongside the company's requirements.
Also by using optical discs to archive data, you will be freeing up valuable disk space, which you would want to keep for live working documents. By storing information offline, you can ensure your data is protected even if something major happens to the server or network.
What to look for when buying an archiving unit
- Speed: The amount of data you have to archive and the amount of time you have available to finish archiving determines the level of performance you need.
- Capacity: The maximum amount of data that can be written to a single tape cartridge/disc/drive. What is the total native and compressed (for tape) capacity?
- Price: Look at the cost per gigabyte in terms of cost of cartridge/native capacity. Cost per gigabyte can vary quite dramatically. Ideally you would want to go for a tape that has a high capacity and is respectably fast and inexpensive.
You should also consider the following questions:
- Will you be randomly accessing files?
If the speed of access to a particular file is of paramount importance then an optical jukebox would be the ideal choice because of their random access capabilities.If you are sequentially archiving data and if you are accessing given files infrequently, then tape technology may be your best bet. This is the prime reason why tape libraries are used by the majority to back up and archive data.
Disk on the other hand is faster than both. You might recall we tested the Quantum DX30 a few months ago. This device can be used in conjunction with a large tape archive unit to give you the best of both worlds being able to quickly restore recent data as well as offload data that is more than a week old (for example) to tape or optical.
- How much data is being stored?
You can easily work out the total capacity of your library by multiplying the media capacity by the number of cartridges or disks the library can accommodate. If you need to archive large amounts of data you would most certainly choose to use tape. LTO 1 tapes can archive up to 200GB of compressed data. Hard disks on the other hand can archive data limited only by your budget, however the media cost per GB is significantly higher. Optical discs can't archive as much data, but have a lower cost per GB than tape or disk.
- How much time do you have to transfer your data?
Archiving a significant amount of data can take longer than you might think. Most tape drives have transfer rates of 15MB per second. This would mean you could archive approximately 216GB in four hours. Optical drives are much slower. They can transfer data at about 2MB per second, which equals 28.8GB in four hours. Hard disks usually transfer data much faster than tape. This is certainly the case with a Quantum DX-30 using fibre channel--45MBps+--but not so much with the Iomega NAS server using gigabit Ethernet we looked at in this review, which clocked in at 8MBps.Many tape and optical libraries have the option of utilising multiple drives, which can increase the throughput by recording several tapes or optical disks simultaneously. You should also make sure the interface you will be using is fast enough to take advantage of the library's full potential. Most likely you will be using some variety of SCSI, but fibre channel and gigabit Ethernet are also popular depending on the circumstances.
- What are your future data storage requirements?
To work out your future storage requirements it would be a good idea if you compared your data storage requirements over the last few years and then estimated your future needs from this data. If it seems like you have to archive twice the amount of data you archived last year, then you could find yourself running out of storage in the near future. The best way to address this problem is to look for libraries that can be expanded.
- What's your budget?
You need to compromise if the library you are considering to buy is the right one but your budget does not allow for it. Another way of looking at things is by looking at the cost of entry versus the cost of usage. Over time you may well see that you have spent more money on media than on the initial hardware.You should also check the warranty and service contracts that the vendors will give you. Take note that many of the drives are not made by the same manufacturer of the library and that the warranties may be different. There are many service levels that are available as well. Try to find a service level that suits your budget and a turnaround time for repairs that is acceptable.
Roadmaps
You will also need to look at scalability. Is it a proven technology that you are buying? Some tape formats for example have been around for years and continue to give us roadmaps but there are others that don't. In these cases you may find yourself with having to purchase more hardware in order to increase your storage capacity.
The main driver in tape technology over the next few years will undoubtedly be the increase in the amount of data stored and archived. This will ultimately mean that archiving has to become more automated, more intelligent, larger, faster, and of course even more reliable than it is today.
The Lynx autoloader we looked at in this review uses LTO 1 tapes. They have a native capacity of 100GB (200GB compressed) and can transfer data at 15MBps in native mode or 30MBps in compressed mode.
There are many tape technologies that are out there. If you are after some more detail on the various types of media that's available we highly recommend you have a look at the April issue of T&B where we cover all the different tape formats that are on the market.
DVD-RAM discs--as used in the JVC jukebox we looked at--were the first rewritable flavour of DVD to come to market, and has subsequently found competition in the rival DVD-RW and DVD+RW formats.
With the same overall size as a standard 120mm diameter, 1.2mm thick CD, DVD discs provide up to 17GB of storage with transfer rates higher than CD-ROM and access times similar to CD-ROM. They come in four versions:
- DVD-5 is a single-sided single-layered disc with a capacity of 4.7GB;
- DVD-9 is a single-sided double-layered disc offering 8.5GB;
- DVD-10 is a 9.4GB dual-sided single-layered disc; and
- DVD-18 will increase capacity to a huge 17GB on a dual-sided dual-layered disc.
The sustained data transfer rates for DVD-RAM is quite low in comparison to disk and tape. JVC claims it can achieve a burst rate of 10MBps and a sustained transfer rate of 2.77MBps (read speeds).
The Iomega NAS uses IDE hard drives to store data, in this case 185.2GB IBM hard disks which spin at 7200RPM. SCSI hard disks on the other hand are faster than IDE drives but are also a lot more expensive. Current SCSI solutions use 36, 73, and even 146GB hard disk drives that operate at 15,000RPM.
