How to calculate disk space requirements for the File System Archiving Option

Article:HOWTO23451  |  Created: 2010-01-01  |  Updated: 2011-11-16  |  Article URL http://www.symantec.com/docs/HOWTO23451
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How to calculate disk space requirements for the File System Archiving Option

Backup Exec requires permanent disk space for the following File System Archiving Option components:

  • Vault store partitions.

  • Indexes

  • SQL Server database

Table: Calculating disk space requirements for the File System Archiving Option components describes the formulas that you can use to estimate the disk space requirements for these components for the File System Archiving Option.

The following values and variables are used in the formulas:

  • N is the number of files.

  • m is the average number of identical copies per file.

    If m is unknown, use the estimate of 1.2.

  • The compression factor for files is estimated as 50%.

    This estimate applies to a mix of files that contain mostly Office 2003 documents. Office 2007 documents do not compress but when mixed with non-Office files, the compression average is 80% of the original size. Pure image files are not compressed.

Table: Calculating disk space requirements for the File System Archiving Option components

Component

Disk space requirements

Vault store partition

You can use the following calculations to approximate the disk space requirements of a vault store partition:

  • Approximate vault store partition size for which single instance storage of archived items is not enabled:

    (N x 4) + (N x average file size in kilobytes x 0.5) kilobytes

  • Approximate vault store partition size for which single instance storage is enabled:

    (N x 4) + ((1/m) x N x average file size * 0.5) kilobytes

For example, you want to know the disk space requirement for a vault store partition for 10,000 files. The average size of each file is 250 KB, and the average number of identical copies per file is 1.2.

If single instance storage of archived items is not enabled, then the calculation for the disk space requirement is as follows:

(10000 x 4) + (100000 x 250 x 0.5) kilobytes = 1.3 GB approximately

If single instance storage is enabled, then the calculation for the disk space requirement is as follows:

(10000 x 4) = ((1/1.2) x 10000 x 250 x 0.5 ) kilobytes = 1.08 GB approximately

Indexes

You can estimate that the index files require approximately 2% of the total size of the files that are archived. The percentage may be less if there is less content to index. If the files are all compressed image file, indexing is less than if the files are mostly small text messages. Numerous small text messages require disk space requirements similar to those of the Exchange Mailbox Archiving Option for indexing

For example, to archive 10 GB of data, at least 200 MB of available disk space is required to store the index files.

Directory database

The Directory database only grows when a new mailbox or share is archived for the first time.

The recommended disk space is 1 GB.

Vault store database

The vault store database grows with every item that is archived. Temporary space is used to hold information on the items that have not been backed up or indexed.

The size of a vault store database is approximately N x 3000 bytes.

Fingerprint database

The fingerprint database is created only if you enable single instance storage of archived items. The fingerprint database holds the shareable parts of archived items. Shareable parts of an item that exceed the single-instance threshold of 20 KB are shared. For the File System Archiving Option, it is expected that all files are larger than the 20-KB threshold.

Backup Exec initially allocates 212 MB for the fingerprint database. The fingerprint database grows with every item that is archived.

If the database grows to more than 212 MB, use the following calculation to estimate the disk space that it requires:

1/m x N x 500 bytes

See About single instance storage of archived items.


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