How to fix ERROR 1021: Disk full; waiting for someone to free some space in MySQL

MySQLINTERMEDIATECRITICALUpdated Dec 22, 2025· 269 views

MySQL ERROR 1021 occurs when the server runs out of disk space while writing data or temporary files. The server will pause operations and wait for space to become available. Fix it by freeing disk space, managing binary logs, redirecting the temp directory, or expanding storage.

Quick fix

Fixes ERROR 1021: Disk full; waiting for someone to free some space

df -h
  1. Check available disk space on all partitions
  2. Check MySQL disk usage in detail
  3. Free up disk space by deleting old data
  4. Purge old binary logs if replication is enabled
mysql — error
df -h
ERROR 1021: Disk full; waiting for someone to free some space

What this error means

MySQL ERROR 1021 (ER_DISK_FULL) is thrown when the MySQL server cannot write to disk because there is insufficient space available. This error typically occurs during write operations like INSERT, UPDATE, ALTER TABLE, or when MySQL creates temporary files for sorting and joining data. The error message usually includes a file path, such as "/tmp/#sql_xxx.MAI" or the MySQL data directory path, indicating where the server was attempting to write when it ran out of space. When this error occurs, the server will pause and wait for disk space to become available before retrying the operation. This is a blocking error that prevents the affected query from completing. The critical issue is that MySQL needs continuous disk space for data files, temporary tables during query execution, binary replication logs, InnoDB transaction logs, and sort operations. If any of these operations consume all available disk space, ERROR 1021 will occur.

Typical symptoms

  • Queries fail with "ERROR 1021: Disk full; waiting for someone to free some space"
  • INSERT, UPDATE, or ALTER TABLE statements hang or fail unexpectedly
  • MySQL server becomes unresponsive during heavy query operations
  • Temporary table operations in /tmp directory fail
  • Replication stops or lags due to binary log growth
  • Application receives "No space left on device" (errno: 28) warnings

Common causes

  1. The disk partition containing MySQL data files (/var/lib/mysql) is completely full
  2. The temporary directory (/tmp) used for sort operations and temporary tables is out of space
  3. Binary log files have grown too large due to unmanaged replication or logging
  4. InnoDB transaction log files or undo logs consuming all available space
  5. Large ALTER TABLE operations creating full table copies in tmpdir
  6. Accumulated database backups or old log files consuming disk space

How to fix "ERROR 1021: Disk full; waiting for someone to free some space"

1Check available disk space on all partitions

First, identify which partition is full using the df command. This shows disk usage across all mounted filesystems and helps identify whether the problem is the main data partition, /tmp, or another location.

bash
df -h

Look for any partition showing 100% usage or very close to it (95%+). The output will show something like:

bash
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       100G   99G  1.0G  99% /
/dev/sda2        50G   50G     0  100% /var/lib/mysql
tmpfs            16G   16G     0  100% /tmp

If multiple partitions are full, you'll need to free space on each one.

2Check MySQL disk usage in detail

Once you know the partition is full, determine which MySQL tables or files are consuming the most space. Log into MySQL and query the information_schema to find the largest tables:

bash
mysql -u root -p

Then run:

sql
SELECT table_name,
       ROUND(((data_length + index_length) / 1024 / 1024), 2) AS 'Size (MB)',
       ROUND(data_length / 1024 / 1024, 2) AS 'Data (MB)',
       ROUND(index_length / 1024 / 1024, 2) AS 'Index (MB)'
FROM information_schema.tables
WHERE table_schema != 'information_schema'
  AND table_schema != 'mysql'
  AND table_schema != 'performance_schema'
ORDER BY (data_length + index_length) DESC
LIMIT 20;

This shows the top 20 tables consuming disk space. Identify tables that may contain old or unnecessary data that can be deleted.

3Free up disk space by deleting old data

Once you identify large tables, delete old records that are no longer needed. This is the safest way to reclaim space without losing critical data.

For example, if you have logs or archived records:

sql
-- Delete records older than 30 days
DELETE FROM logs WHERE created_at < DATE_SUB(NOW(), INTERVAL 30 DAY);

-- Or clear specific archive tables
TRUNCATE TABLE archived_transactions;

-- After deleting, optimize the table to reclaim space
OPTIMIZE TABLE logs;

The OPTIMIZE TABLE command rebuilds the table and removes fragmentation, reclaiming unused space from deleted rows. For InnoDB tables, this temporarily requires additional disk space, so ensure you have some free space first.

4Purge old binary logs if replication is enabled

If MySQL replication is enabled, binary logs can consume significant disk space. Check the current binary logs and purge old ones:

sql
-- Show current binary logs
SHOW BINARY LOGS;

-- Purge logs older than 7 days
PURGE BINARY LOGS BEFORE DATE_SUB(NOW(), INTERVAL 7 DAY);

-- Or purge before a specific date
PURGE BINARY LOGS BEFORE '2024-01-15';

To automatically purge binary logs, add this to your MySQL configuration file (/etc/mysql/my.cnf):

ini
[mysqld]
binlog_expire_logs_seconds = 604800  # 7 days in seconds
# Or use the older directive (deprecated in MySQL 8.0.3)
expire_logs_days = 7

Restart MySQL to apply the changes:

bash
sudo systemctl restart mysql
5Clear temporary files in /tmp directory

MySQL uses the /tmp directory (or a custom tmpdir) for temporary tables during sort operations and complex queries. If /tmp is full, clear old temporary files:

bash
# Show temp directory usage
du -sh /tmp

# Remove MySQL temporary files (if MySQL is stopped)
sudo rm -rf /tmp/#sql_*

# Or use tmpwatch to safely remove old files (older than 24 hours)
sudo tmpwatch 24 /tmp

If you need to change the temporary directory to a larger partition, update the MySQL configuration:

bash
# Create a new tmpdir with adequate space
sudo mkdir -p /mnt/bigssd/mysql_tmp
sudo chown mysql:mysql /mnt/bigssd/mysql_tmp
sudo chmod 750 /mnt/bigssd/mysql_tmp

Then update /etc/mysql/my.cnf:

ini
[mysqld]
tmpdir = /mnt/bigssd/mysql_tmp

Restart MySQL:

bash
sudo systemctl restart mysql
6Expand disk space if freeing space is insufficient

If freeing up space doesn't resolve the issue, or if the database is legitimately large, you need to expand available disk space.

For cloud environments (AWS, Azure, Google Cloud), you can expand the disk volume:

bash
# For AWS EBS, expand the volume in the console, then resize the filesystem
sudo resize2fs /dev/xvda1

# For Azure managed disks, expand in the portal, then resize
sudo parted /dev/sda
# Type: resizepart
# Number: 1
# End: 100%
sudo resize2fs /dev/sda1

For physical servers, you can add additional storage or move the MySQL data directory to a larger partition:

bash
# Stop MySQL
sudo systemctl stop mysql

# Move data directory
sudo mv /var/lib/mysql /mnt/large_disk/mysql

# Update MySQL config
# Edit /etc/mysql/my.cnf and change:
# datadir = /mnt/large_disk/mysql

# Fix permissions
sudo chown -R mysql:mysql /mnt/large_disk/mysql

# Restart MySQL
sudo systemctl start mysql
7Monitor disk usage to prevent future issues

Set up monitoring to catch disk space issues before ERROR 1021 occurs.

Create a cron job to alert when disk usage exceeds 80%:

bash
# Add to crontab (crontab -e)
0 */4 * * * df -h | grep -vE '^Filesystem|tmpfs|cdrom' | awk '{ print $5 " " $1 }' | while read output; do
  usage=$(echo $output | awk '{ print $1}' | cut -d'%' -f1)
  partition=$(echo $output | awk '{ print $2 }')
  if [ $usage -ge 80 ]; then
    echo "WARNING: $partition is $usage% full" | mail -s "Disk Alert" admin@example.com
  fi
done

Alternatively, use cloud monitoring (CloudWatch for AWS, Azure Monitor, etc.) to set up automatic alerts.

Keep at least 20% free disk space at all times to allow MySQL sufficient room for temporary operations, index updates, and growth.

Advanced notes

InnoDB-specific considerations: If using InnoDB, the tablespace can become fragmented. While you cannot shrink the InnoDB data files without full dump/restore, you can add new data files and InnoDB will balance data across them:

sql
ALTER TABLESPACE innodb_system ADD DATAFILE '/mnt/large_disk/mysql_data2.ibd' FILE_BLOCK_SIZE=16K;

Temporary table locations: Some queries generate temporary tables in memory, but complex sorts fall back to disk. Increase tmp_table_size and max_heap_table_size to keep more temporary tables in memory:

sql
SET GLOBAL tmp_table_size = 536870912;  -- 512MB
SET GLOBAL max_heap_table_size = 536870912;  -- 512MB

Running queries during low disk: If ERROR 1021 occurs while a query is running, MySQL will wait indefinitely. To resume, simply free disk space (delete files, purge logs, etc.), and the query will automatically continue after a few seconds.

Multi-partition setups: If you have separate partitions for data and logs (/var, /tmp, /var/lib/mysql), check all of them. A full /var partition can prevent logging, which can also trigger ERROR 1021 indirectly. The most common culprit is /tmp during large ALTER TABLE operations or complex sorts.

Frequently asked questions

What does "ERROR 1021: Disk full; waiting for someone to free some space" mean?
MySQL ERROR 1021 (ER_DISK_FULL) is thrown when the MySQL server cannot write to disk because there is insufficient space available. This error typically occurs during write operations like INSERT, UPDATE, ALTER TABLE, or when MySQL creates temporary files for sorting and joining data. MAI" or the MySQL data directory path, indicating where the server was attempting to write when it ran out of space.
How do I fix "ERROR 1021: Disk full; waiting for someone to free some space"?
MySQL ERROR 1021 occurs when the server runs out of disk space while writing data or temporary files. The server will pause operations and wait for space to become available. Fix it by freeing disk space, managing binary logs, redirecting the temp directory, or expanding storage.
What causes "ERROR 1021: Disk full; waiting for someone to free some space"?
The disk partition containing MySQL data files (/var/lib/mysql) is completely full The temporary directory (/tmp) used for sort operations and temporary tables is out of space Binary log files have grown too large due to unmanaged replication or logging
Is the "ERROR 1021: Disk full; waiting for someone to free some space" error serious?
Yes. This is a critical-severity error that usually blocks work until it is fixed, but the steps above resolve it.

Official resources & further reading