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Backup size reporting

Overview

Percona XtraBackup reports the size of every successful backup in xtrabackup_info and reports the same values in the XtraBackup error log.

Backup size reporting helps estimate storage requirements, check that backups work correctly, and plan restores for compressed and streamed backups.

Version changes

Percona XtraBackup 8.4.0-6 introduces backup size reporting.

Why external tools cannot accurately measure backup size

External tools cannot reliably determine the final size of XtraBackup output in many backup configurations.

Backup size often differs from the MySQL datadir size because Percona XtraBackup also copies redo log data generated during the backup process.

Several backup features further change the final output size:

  • --stream=xbstream adds xbstream metadata

  • --compress reduces the final backup size according to data compressibility

  • Sparse InnoDB tablespaces affect filesystem size reporting

  • Streaming and cloud uploads may not produce local backup files for measurement

  • Compression, encryption, and streaming pipelines prevent external tools from accurately calculating final backup size

Compressed backups also require sufficient free space during decompression and restore. Reporting the uncompressed backup size helps estimate restore storage requirements before recovery operations begin.

How backup size reporting works

Percona XtraBackup records backup size at the end of every successful backup. Backup size reporting is enabled by default and requires no additional configuration.

Percona XtraBackup calculates backup size after all backup operations complete, including:

  • Compression

  • Encryption

  • xbstream formatting

  • Sparse file handling

For sparse InnoDB tablespaces, Percona XtraBackup counts only written data fragments and excludes filesystem hole ranges.

The reported backup size matches the exact number of bytes written to the backup destination.

Compressed backups additionally report:

  • uncompressed_backup_size

  • Compression ratio

Percona XtraBackup calculates uncompressed_backup_size separately from the final compressed backup size so that the reported value reflects the logical backup size before compression.

Percona XtraBackup stores the reported values in:

  • xtrabackup_info

  • XtraBackup error log

Reported values

Field Description
backup_size Final backup output size in bytes
uncompressed_backup_size Total uncompressed logical backup size in bytes
Compression ratio Ratio between uncompressed_backup_size and backup_size reported in the XtraBackup error log

xtrabackup_info

Percona XtraBackup writes backup size metadata to xtrabackup_info in the backup output.

Depending on backup configuration, xtrabackup_info in the backup output may be:

  • Plaintext

  • Compressed

  • Encrypted

  • Embedded inside an xbstream archive

Streamed backups store xtrabackup_info inside the xbstream output.

If xtrabackup_info is not plaintext, you can create a separate plaintext copy of xtrabackup_info using the --extra-lsndir=<dir> option.

Note

Files created in the --extra-lsndir=<dir> directory are not part of the backup.

XtraBackup error log

Percona XtraBackup prints information about backup size near the end of the backup operation before the completed OK! message.

The log output includes:

  • Human-readable size

  • Exact byte count

  • Compression ratio

Output

Uncompressed backup example

The following example shows xtrabackup_info from a backup created with --target-dir.

uuid = 122a291d-48b0-11f1-9d76-047bcbcb6b7e
name =
tool_name = xtrabackup
tool_command = --backup --no-defaults --user=root --socket=/tmp/pxb-folder/mysql.sock --target-dir=/tmp/pxb-folder/backup --extra-lsndir=/tmp/pxb-folder/lsndir --datadir=/tmp/pxb-folder/datadir
tool_version = 8.4.0-6
ibbackup_version = 8.4.0-6
server_version = 8.4.8-8
server_flavor = Percona Server (GPL), Release 8, Revision 1c288264
start_time = 2026-05-05 19:27:26
end_time = 2026-05-05 19:27:28
lock_time = 0
binlog_pos = filename 'binlog.000002', position '158'
innodb_from_lsn = 0
innodb_to_lsn = 24785178
partial = N
incremental = N
format = file
compressed = N
encrypted = N
lock_ddl_type = ON
backup_size = 88689086

The XtraBackup error log contains the corresponding backup size entry:

2026-05-05T19:27:28.140024+01:00 0 [Note] [MY-011825] [Xtrabackup] Backup size: 84.58 MiB (88689086 bytes)
2026-05-05T19:27:29.382428+01:00 0 [Note] [MY-011825] [Xtrabackup] completed OK!

Compressed backup example

Compressed backups additionally report the uncompressed backup size and compression ratio.

The following example shows the final lines of xtrabackup_info with backup size values reported in bytes:

backup_size = 1832398
uncompressed_backup_size = 88689148

The XtraBackup error log contains the corresponding output:

2026-05-05T19:27:42.851038+01:00 0 [Note] [MY-011825] [Xtrabackup] Backup size: 1.75 MiB (1832398 bytes)
2026-05-05T19:27:42.851055+01:00 0 [Note] [MY-011825] [Xtrabackup] Uncompressed backup size: 84.58 MiB (88689148 bytes)
2026-05-05T19:27:42.851065+01:00 0 [Note] [MY-011825] [Xtrabackup] Compression ratio: 48.40x

Percona XtraBackup calculates the compression ratio as:

uncompressed_backup_size / backup_size