This document contains basic information about snapshot backups and the technology behind it. It is our hope that this document will allow a business executive to have a basic understanding of how this technology works and how implementing snapshot backups can potentially disrupt OASIS in their environment.
OASIS has utilized the SAP Sybase SQL Anywhere database engine (formerly Sybase Adaptive Server Anywhere) for over 15 years. When OASIS was first being developed by Ingen Software, VSS wasn't available so it was not considered in the original specifications for the server portion of OASIS. It wasn't until Windows XP and Windows Server 2003 were released that this technology was available. SAP/Sybase did not support VSS against a SQL Anywhere database until version 10 of the database software.
As virtualization has become a more standard practice, software has been developed to create incremental backups called snapshots for entire virtual machines instead of just individual files. This has led to better options for rapid recovery in the event of a hardware failure, data corruption, or malware infections.
What is VSS?
VSS, also known as Volume Snapshot Service, Volume Shadow Copy Service, or Shadow Copy, is a technology from Microsoft that is used to create backup copies of files or whole NTFS formatted volumes, and can be utilized while the files or volumes are in use. Certain applications must be "VSS Aware" so that when VSS issues a "freeze" command for a file that is in use, the application will stop making changes to the file so a valid copy can be made. Then a "thaw" command is issued by VSS so that normal file operations can resume.
The SAP Sybase SQL Anywhere database utilized by OASIS is not VSS aware by default but it can be made VSS aware through the additional setup step of adding the SQL Anywhere VSS writer service.
Issues we have seen with snapshot backups
- Partial corruption of a live database
- This requires recovery from a backup or by manual unload and reload of tables resulting in some data loss.
- Total corruption of a live database
- The database file was several hundred GB, then dropped to 0 bytes.
- Corruption of the live transaction log
- This caused the database to be unable to start.
- Non-viable backups that are not able to start or be recovered
- This results in much longer recovery times because an "easy" recovery is no longer possible.
When doing initial setup, the Oasis Support Team will typically add the SQL Anywhere VSS Writer service whether it is needed or not. This allows for safe VSS snapshots to be taken. If this was not done, it can be added at any time without any impact to the end users.
If you have snapshots enabled in your environment, it is still recommended to use the built in daily backup as part of your layered backup solution. In the event of a database failure, the Oasis Support Team can use an older database copy and the daily transaction logs to roll the copy forward up to current data as long as all logs are available.