Why Does a NAS Report Free Space but Reject New Large Files?

A NAS can show free capacity yet reject a large file when the destination’s quota, metadata, file limit, or writable allocation is exhausted.

The dashboard may report pool-wide space while the share belongs to a smaller dataset, thin volume, user quota, reserved filesystem, or nearly exhausted metadata profile. A large upload may also require temporary space, a second copy, or a single-file size that the destination filesystem cannot represent. Begin with the exact failing path and error code instead of assuming the headline free-space number describes the operation.

Identify Which Filesystem and Limit the Share Actually Uses

Resolve the SMB or application share to its host path, mountpoint, dataset, subvolume, thin volume, and underlying pool. Record free blocks, free inodes, user identity, and the size of the rejected file.

GNU explains that df reports the mounted filesystem associated with a path, not every pool, quota, snapshot, or application-level limit above and below it.

If the share writes to a system partition or smaller mounted dataset, pool-wide free space is irrelevant. Correct the path or mount before deleting data from the wrong storage layer.

Check User, Group, Dataset, and Share Quotas

Compare the administrator’s free-space view with the quota applied to the actual SMB user, group, dataset, project, or shared folder. Test with the same account that receives the error.

Oracle documents that ZFS quotas and reservations can limit one dataset even while unused pool space remains or reserve available capacity for another dataset.

Do not remove quotas globally. Increase only the proven limit or move the file to a dataset whose capacity policy matches the workload.

Compare Data Space With Metadata and Allocation Workspace

Inspect data, metadata, system allocation, block groups, and filesystem-specific reservation counters. Large-file creation may need metadata updates and copy-on-write workspace in addition to payload bytes.

Btrfs documentation notes that it can return ENOSPC despite visible free space when its allocation and copy-on-write requirements cannot be satisfied.

If metadata is constrained, use supported filesystem diagnostics and narrow recovery actions. Do not fill the remaining space with another large test file or start an unfiltered balance without measuring workspace.

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Check Inodes and File-Record Limits

Record free inodes or file records and count small files in caches, mail stores, thumbnails, extracted packages, and application directories. Large byte capacity does not guarantee another directory entry or metadata record can be allocated.

Red Hat’s filesystem overview explains that XFS dynamically allocates inodes and that filesystem implementations have distinct inode and file-record limits.

If inodes are exhausted, remove or archive a verified high-count cache through the application that owns it. Deleting one large file will not solve a file-record shortage.

Verify the Destination’s Maximum File Size and Format

Identify the destination filesystem and compare its maximum single-file size with the attempted upload. Include removable staging disks, USB backup destinations, and application temporary folders.

Microsoft’s NTFS overview shows that maximum file size depends on filesystem design and allocation parameters, so aggregate free space does not override a single-file format limit.

If the failure occurs near a consistent boundary such as 4GB, inspect every intermediate filesystem and upload path. Reformatting destroys data, so migrate verified files elsewhere before changing the destination format.

Measure Temporary, Sparse, and Preallocation Requirements

Check whether the uploader writes a temporary file, preallocates the full destination, keeps the old version until rename, or unpacks an archive into additional files. Record peak allocation rather than final file size.

The fallocate system call reserves disk space so later writes do not fail for lack of capacity, which means an application can reject a large file before transferring all of its data.

Choose a temporary directory on the intended data pool or disable preallocation only when the application supports it safely. Keep enough headroom for the original, temporary copy, metadata, and snapshots during replacement.

Reproduce the Exact Error With a Controlled File

Create test files below and above the failing size using the same user, protocol, path, and application. Capture the client error and server log without repeatedly retrying the production file.

The ZimaSpace guide to finding unexpected NAS space use provides the adjacent method for reconciling visible folders with actual filesystem allocation.

The issue is resolved when the proven quota, metadata, inode, format, or temporary-space limit is corrected and a file above the former failure size writes, closes, reopens, and verifies successfully. Stop writes if the filesystem becomes read-only or reports corruption or hardware errors.