apache/cassandra · critical · RuntimeException

Not enough disk space to store %s

Error message

Not enough disk space to store %s

What it means

If no specific directory was determined for the descriptor, getWriteDirectory asks Directories.getWriteableLocation(estimatedWriteSize) for any data directory with enough free space. A null return (no directory can hold the estimated output) triggers a RuntimeException stating the required size. This prevents starting a compaction that would inevitably fail mid-write.

Source

Thrown at src/java/org/apache/cassandra/db/compaction/writers/CompactionAwareWriter.java:302

                logger.trace("All sstables not from the same disk - putting results in {}", descriptor.directory);
                break;
            }
        }
        Directories.DataDirectory d = getDirectories().getDataDirectoryForFile(descriptor);
        if (d != null)
        {
            long availableSpace = d.getAvailableSpace();
            if (availableSpace < estimatedWriteSize)
                throw new RuntimeException(String.format("Not enough space to write %s to %s (%s available)",
                                                         FBUtilities.prettyPrintMemory(estimatedWriteSize),
                                                         d.location,
                                                         FBUtilities.prettyPrintMemory(availableSpace)));
            logger.trace("putting compaction results in {}", descriptor.directory);
            return d;
        }
        d = getDirectories().getWriteableLocation(estimatedWriteSize);
        if (d == null)
            throw new RuntimeException(String.format("Not enough disk space to store %s",
                                                     FBUtilities.prettyPrintMemory(estimatedWriteSize)));
        return d;
    }

    public CompactionAwareWriter setRepairedAt(long repairedAt)
    {
        this.sstableWriter.setRepairedAt(repairedAt);
        return this;
    }

    protected long getExpectedWriteSize()
    {
        return cfs.getExpectedCompactedFileSize(nonExpiredSSTables, txn.opType());
    }

    /**
     * It is up to the caller to set the following fields:
     * - {@link SSTableWriter.Builder#setKeyCount(long)},

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Free space across data directories: drop unneeded snapshots, run nodetool cleanup, truncate/TTL-expire data.
2. Add storage capacity or additional data directories.
3. Lower estimated write pressure by tuning compaction strategy (smaller compaction targets).
4. Check disk_usage settings and monitoring to catch trends before writes fail.

Example fix

// before (shell)
# all data dirs < estimatedWriteSize free; compaction throws
// after (shell)
nodetool clearsnapshot --all && df -h /var/lib/cassandra  # verify free space before retrying

// cluster check before heavy compaction
for (String dir : dataDirs) if (new File(dir).getUsableSpace() < minRequiredBytes) alert();

try {
    compact();
} catch (RuntimeException e) {
    if (e.getMessage().startsWith("Not enough disk space")) { scaleStorage(); }
    else throw e;
}

When it happens

Trigger: A compaction calls defaultLocation -> getWriteDirectory when no data directory has at least estimatedWriteSize free (all disks below the blacklisting threshold for the requested size).

Common situations: Cluster-wide disk pressure, one-node disks filled by hints/snapshots, or very large estimated output after a burst of writes.

Related errors

• Not enough space to write %s to %s (%s available)
• Not enough space for compaction (%s) of %s.%s, estimated sst
• Only {} free across all data volumes. Consider adding more c
• concurrent_compactors should be strictly greater than 0, but
• Cannot DROP COMPACT STORAGE as some nodes in the cluster (%s

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/64069ba92e3ad742. Report an issue: GitHub.