About backups

 

Related Topics

 

 

A backup is an electronic copy of the files installed on your computer systems. Your H2OS installation is a subset of your entire computer installation, both of which should be backed up and the backups cycled off-site on a regular, systematic basis. This topic focuses on your H2OS database installation and it's backup requirements only. In addition to a backup system for your H2OS database, you will also need a backup strategy for your computer installation as a whole, which is beyond the scope of H2OS backups.

 

This section contains topics related to backing up your data, and H2OS procedures for handling this crucially important aspect of computing.

 

In this topic:
 

 

  1. The importance of backups

  2. H2OS backups are for restoring H2OS only

  3. In addition to H2OS backups

  4. Backups are stored as compressed files

  5. More information

 

 

 

The importance of backups

 

If you're a firm believer in backups, please skip this topic.

 

Please believe us when we say that the last thing we want to say to you is that database damage requires restoring a backup.

 

And then, imagine that you don't have a recent backup.  

 

Woe is you!

 

Let's never let it get to this point. The solution is relatively simple: run your backups religiously, and then take care of them. Always put your backups on physical media such as DVD and keep them safe in an off-site location.  

 

Database installations in particular depend upon being properly backed up at all times. This is because databases are collections of files that are related to each other in sometimes non-obvious ways (until something doesn't work) making them very sensitive to files being kept in sync with each other at all times.  

 

The strength, utility and power of your computer systems is directly related to how well you create, handle and secure backup copies of your data and how well you practice system management disciplines. In the event of a data loss, you will need to recover your database (and other files) to the most recent date/time available.  

With a properly setup and functioning backup system, your computer systems and databases will suffer less loss in the event of a system failure, and often your computers will be are back up and running shortly after the event. A mismanaged backup system, on the other hand, can be very problematic if it's discovered that needed data is not available in the backups.

 

Be fastidious about your backups!

 

Modern hard drives have "mean time between failure" (MTBF) ratings into many thousands of hours. This can create a deceiving situation, because in the end all machines will eventually fail. It's really a question of when, not if.  It's at this moment that your handling of backups will come to the fore.

 

Bear in mind that it doesn't matter how many backups you have in your library. What's of the greatest importance after a catastrophic failure, is how recent is your last backup - because that's the one you'll need to restore to.

 

When it comes to your backups, think regular, frequent, verified and off-site. It is an imperative for successful computer operations that your administrator perform regularly scheduled backups, and properly store your backups (off-site). In addition, to insure the integrity of your backups, we strongly advise you to periodically retrieve and test the readability of selected (typically most recent, but also older backups from time to time as well) to insure they will be available and useful when needed.

 

All hard drives will eventually fail

The availability of very large capacity and highly reliable hard drives are wonderful things, but the high MTBF (Mean Time Between Failure) numbers advertised by manufacturers can create an illusion that backups are no longer necessary. This is not true. All machines will fail eventually. Partial hard drive failures can also occur, which can render from one to 'any number' of files hopefully corrupted and unusable.

 

The most difficult aspect of hard drive failures is that you often have no warning at all. "It worked this morning, and completely unusable this afternoon" is one worst case scenario. When such a problem does occur, the first indication you may see is a message pertaining to Windows or H2OS not being able to find or read a file.

 

It's beyond the scope of this topic, and H2OS support, to help you determine the nature and extent of the problem itself, but if you determine that you have experienced a hard drive failure, your first reaction may (should) be to take a backup NOW, if you can, to capture as many files from the drive as possible, and as quickly as possible. All well and good, but keep in mind this is data that wasn't damaged or lost by the event. To recover from the failure you will need to restore from a backup taken before the event.  

 

Note that there are companies  who specialize in retrieving data from failed hard drives, but they are very expensive and not always complete.

 

What exacerbates this problem for database systems such as H2OS is the fact that databases are not contained in single files, but are collections of inter-related files which can exist on more then one hard drive and across your network.  Regardless of physical location, they are part of the logical database, and each file depends upon the integrity of the others for the database to work correctly. This is true regardless of the underlying software and technologies used.

 

To the extent that  your backup regime is functioning and properly managed, to the same extent disruption caused by the failure of a hard drive can be minimized.

 

 

 

Hardware and network failures (even "hiccups") can corrupt databases

Databases consist of multiple files that are in a continuous state of synchronization with each other. Index files for example must be in continuous sync with the table using the index. It is possible for a hardware or network failure to corrupt an index file and thus render the related table unusable. In some cases the database can become unusable.

 

In cases where one or a small number of files are identified as having become corrupted (and you are sure these are the only files), recovery can be performed by restoring the files from your most recent backup, and manually making changes to the files as needed.

 

If more than a few identifiable files are involved, or you are unsure, then it will may bebe necessary to do a full database restore to an earlier point in time.

 

H2OS includes design features intended to make it fault tolerant, in particular the use of buffering techniques that reduce the system's exposure to hardware failures to moments in time rather then extended periods of time. Nevertheless, it is possible for a failure to occur at just the wrong moment. All computer systems share this vulnerability due to the need to keep certain data in sync with other data, and any interference with mutually dependent sequences of operations can have catastrophic consequences.

 

 

Instructive war stories abound on the Internet. Here is a link to some computer disaster stories (scroll down to reader comments)

 

 

Backup frequency

 

When deciding a backup frequency consider that when a hard drive does fail, it doesn't matter at all that it performed perfectly for years, or that you have tons of backups of the drive for earlier dates.  What matters now is "how old is our last backup?".  This is because after restoring the backup you will need to manually re-enter new records, changes, etc. that were made in the time frame between the event and the date/time of the restored backup.

 

How often should you take backups?

 

For one thing, if you don't trust your hardware, software or network, then backup daily or even more often. If you have a hard drive making noise, for example, until it can be replaced you may want to backup very often, maybe hourly.

 

If your systems are stable, you may with the opt for daily backups.

 

Whatever frequently you decide, the important part is that you stick with it religiously.

 

If you have H2OS installed in a LAN configuration remember that the backup must be taken on the server and that all H2OS workstations must be logged off H2OS before running the backup.

 

 

 

 

2. H2OS backups are for restoring H2OS only

 

H2OS created backups are NOT COMPLETE. They contain only database tables that are changed in ongoing H2OS operations. Static (reference, look-up) tables are not included, nor are executables. Basically, files that we can provide replacements for are excluded from H2OS created backups. This is done to reduce the size of backup files, and to save time creating and transferring them.

 

Thus it is important to understand that H2OS backup and restore procedures are designed to backup and restore only your update-able H2OS database tables.

 

You cannot use backup/restore to transfer an H2OS installation from one computer to another because the original H2OS installation involves registry changes and possibly the installation of some Microsoft Windows System files (which we are basically required by Microsoft to distribute with our software). These files are NOT included in H2OS created backups.

 

In the event of a computer or hard drive level failure, you will need to restore the hard drive from your backups, then re-install H2OS, and then restore your most recent H2OS backup, in this order.

 

It is at this moment that you will either benefit from being fastidious about your backups,or have been lax and now have to scurry to catch your database up with missing data entered since the last complete backup was taken. It's very much a "pay me now or pay me later" situation.

 

 

3. In addition to H2OS backups

 

H2OS backups are a subset of your installations backup strategy. Beyond backing up your H2OS database, you will need a backup strategy that includes all of the computers in your installation.

 

For hard drive level backups, there are products on the market that will backup hard drives in such a way that they can be restored onto new hard drives.

 

 

 

4. Backups are stored as compressed files

 

H2OS backups are compressed using the ZIP format. Using this format makes downloading files from the Internet faster and allows software distributors to put more files on distribution media, such as a CD. Most zipped files end with the .zip extension.

 

You may have a ZIP compression software product such as WinZip installed, and Windows XP and higher has a built-in standard utility for unzipping files.

 

 

More information

 

 

Some links to websites with information about backups

 

WIkipedia's definition of backup

 

Why backups are so important
 

Three reason why backups are important

 

Dealing with the Complexity of Storage Systems

 

A list of backup software products

 


A write-up Hewlett Packard

http://static.highspeedbackbone.net/pdf/hp_why_backup.pdf