What Is RAID? UGREEN NAS RAID Types Explained

RAID, or Redundant Array of Independent Disks, combines multiple drives into one logical storage pool. Depending on the RAID level, it uses striping, mirroring, parity, or a combination of these methods to balance capacity, performance, and drive-failure tolerance.

UGOS Pro supports seven storage modes: Basic, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10.

RAID protects against specified drive failures. It cannot recover files that were deleted, overwritten, encrypted by ransomware, or lost with the NAS itself.

Quick Answer: Which UGREEN NAS Storage Mode Should You Use?

Before creating the pool, consider how many drives you have, how much usable capacity you need, how quickly a failed drive can be replaced, and whether the data exists anywhere else.

How Does RAID Work?

Three storage techniques explain the differences between RAID levels.

Striping

Striping divides data across multiple drives so the members can read or write in parallel. It can increase throughput, but striping by itself provides no drive-failure protection.

RAID 0 uses striping without mirroring or parity.

Mirroring

Mirroring writes identical data to multiple drives. If one member fails, another member still contains a complete copy.

RAID 1 uses mirroring, while RAID 10 creates multiple mirrored pairs and stripes data across them.

Parity

Parity stores calculated recovery information across the array. If a drive fails, the system uses the surviving data and parity to reconstruct the missing information.

RAID 5 uses single distributed parity. RAID 6 uses dual distributed parity, allowing it to survive any two member-drive failures.

These mechanisms also explain why Basic, JBOD, and RAID 0 carry more risk than the redundant storage modes.

Basic, JBOD, and RAID 0: Storage Without Redundancy

Basic, JBOD, and RAID 0 organize drives differently, but none keeps your data available after the relevant member failure.

Basic: One Drive and One Storage Pool

Basic creates a storage pool from one drive. It provides the available capacity of that drive without redundancy.

Basic is reasonable when:

• The NAS currently contains only one drive.
• The data is another copy of files stored elsewhere.
• The content can be downloaded or recreated.
• You plan to add drives and migrate through a supported path later.

It is a poor choice for the only copy of family photos, business documents, or an active project.

Adding a second drive does not protect an existing Basic pool by itself. The pool must be migrated to RAID 1 before the second drive provides mirroring.

JBOD: Combining Drives Without Redundancy

JBOD combines multiple drives into one storage pool without striping or parity. It can make mixed-capacity drives easier to manage as one space, but it provides no recovery guarantee.

Treat the entire JBOD pool as being at risk if any participating drive fails.

JBOD is suitable for replaceable downloads, temporary archives, or other data that already exists elsewhere. Separate Basic pools are a better option when you want a failure on one drive to remain isolated from data stored on another.

RAID 0: Speed Without Protection

RAID 0 stripes data across at least two drives. With matching drives, it uses their combined capacity and can increase sequential throughput.

The cost is complete array dependence. Because each file is divided across the members, one failed drive makes the entire RAID 0 pool unreadable.

Use RAID 0 for:

• Render cache
• Temporary video exports
• Scratch data
• Test environments
• Another workload that can be recreated

Network speed can hide RAID 0’s performance advantage. A 1GbE connection delivers roughly 110 MB/s during practical file transfers, which a single modern hard drive can already reach during sequential reads. RAID 0 becomes more relevant over 2.5GbE or 10GbE when the client, network, protocol, and workload can also sustain the additional speed.

When important data must remain available after a drive failure, start with a redundant mode.

RAID 1: The Practical Default for a Two-Drive NAS

RAID 1 writes identical data to two drives. If either member fails, the surviving drive retains a complete copy and the storage pool can remain available while you prepare a replacement.

This makes RAID 1 a strong fit for a two-drive UGREEN NAS holding:

• Family photos and videos
• Computer backups
• Documents
• Personal files
• Home media libraries
• Small-business shared folders

Two matching 8TB drives provide exactly 8TB of decimal data capacity in RAID 1. UGOS Pro displays the binary-converted value with the TB label, so the pool appears as roughly 7.3TB before the system reservation and file-system overhead. The difference between 8TB and 7.3TB is unit conversion, not missing storage.

Replace a failed RAID 1 member promptly. Once one drive fails, the mirror has no remaining redundancy. A problem with the surviving member during rebuilding can cause data loss.

RAID 1 also reproduces file changes across both drives. If a user deletes a folder or ransomware encrypts it, both members reflect that change. Mirroring protects availability after drive failure; it does not preserve an earlier version of the file.

Two drives are enough for mirroring. With three or more drives, parity can preserve more usable capacity.

RAID 5: More Usable Capacity from Three or More Drives

RAID 5 stripes data and distributed parity across at least three drives. It uses the equivalent capacity of one member for parity and tolerates one drive failure.

Its decimal data-capacity formula is:

(number of drives - 1) × capacity of the smallest drive

RAID 5 is a practical fit when:

• Three or more matching drives are installed.
• Capacity efficiency matters.
• One-drive fault tolerance is acceptable.
• The workload consists mainly of file storage, backups, media, or creative archives.
• Important files also have an independent backup.

Four matching 8TB drives provide exactly 24TB of decimal data capacity in RAID 5. The interface displays roughly 21.8TB before the system reservation and file-system overhead.

The RAID 5 Rebuild Window

After one member fails, a RAID 5 array becomes degraded and has no redundancy left. Rebuilding requires extensive reads from every surviving drive while reconstructing the missing data on the replacement.

Large drives can leave the array in this vulnerable state for hours or days. Performance can also fall while the rebuild competes with normal workloads.

An unrecoverable read error on a surviving member can prevent affected data from being reconstructed. IBM’s analysis of RAID 5 and RAID 6 rebuilds explains how the amount of data read, drive error specifications, and rebuild duration affect that risk.

Published nonrecoverable read-error specifications vary by exact drive model. Compare the manufacturer’s specification for each drive instead of assigning one failure rate to every desktop or NAS drive. Use compatible CMR drives designed for the expected workload, and consult our NAS drive-selection guide before building the array.

If one-drive tolerance is not enough, RAID 6 and RAID 10 offer two different ways forward.

RAID 6 vs. RAID 10

RAID 6 and RAID 10 both require at least four drives, but their protection, performance, and rebuilding behavior differ.

RAID 6 for Predictable Two-Drive Protection

RAID 6 can tolerate any two member-drive failures. That protection becomes more valuable in six-drive and eight-drive systems, with large-capacity drives, or when replacing a failed member may take time.

RAID 6 performs more parity work than RAID 5. Small random writes are particularly sensitive to that overhead, although actual performance also depends on the processor, drives, array size, workload, and network.

Six matching 8TB drives provide 32TB of decimal data capacity in RAID 6. The same six drives provide 24TB in RAID 10.

RAID 10 for Write-Heavy Workloads

RAID 10 stripes data across mirrored pairs. It suits virtual machines, databases, application data, and active project files with frequent random reads and writes.

Rebuilding normally copies data from the surviving mirror partner rather than recalculating distributed parity across all remaining members. Drive capacity, health, workload, and the amount of stored data still determine how long the rebuild takes.

RAID 10 does not guarantee survival of every two-drive failure. If both members of the same mirror pair fail, the array fails.

On a four-drive NAS, RAID 6 and RAID 10 both use half of the raw capacity. Choose RAID 6 when surviving any two member failures matters most. Choose RAID 10 when write performance and mirror-based recovery matter more.

How Much Usable Capacity Does Each RAID Level Provide?

RAID capacity is normally calculated using the smallest participating drive.

These formulas show data capacity before the UGOS Pro system reservation, file-system metadata, snapshots, and other overhead.

Four Matching 8TB Drives

Drive manufacturers define 1TB as 1,000,000,000,000 bytes. Operating systems commonly calculate the displayed figure using binary units while still labeling it TB. That conversion is why 24TB appears as roughly 21.8TB. System and file-system overhead reduce the final available space further.

Use the UGREEN RAID Calculator to compare your planned drive count, capacities, protection allocation, and unused space.

What Mixed Drive Sizes Cost You

Consider a RAID 5 pool containing one 8TB drive and three 16TB drives:

• Installed raw capacity: 56TB
• Capacity recognized as four matching 8TB members: 32TB
• Data capacity after parity: 24TB
• Capacity allocated to parity: 8TB
• Capacity stranded by the size mismatch: 24TB

The difference between 56TB purchased and 24TB usable is 32TB. Of that difference, 8TB is the parity allocation required by RAID 5. The remaining 24TB is unavailable because each 16TB member is limited to the capacity of the 8TB drive.

Matched drive capacities make utilization, replacement, and expansion easier to predict.

Which RAID Levels Do UGREEN NAS Models Support?

UGREEN NAS enclosures are sold diskless, so the installed drives and selected storage mode determine the final usable capacity.

The mode available for a specific storage pool still depends on the number of drives included in that pool. M.2 SSDs used as cache do not participate in the SATA RAID. When M.2 SSDs form a separate storage pool, its available modes depend on the number of installed SSDs.

Once you know the drive count and RAID level you need, browse and filter UGREEN NAS models by bay count, networking, SSD support, and workload.

Does UGREEN NAS Support SHR, RAID F1, ZFS, or RAID-Z?

No. UGREEN NAS does not support SHR, RAID F1, ZFS, or RAID-Z. UGOS Pro provides Basic, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10.

SHR and RAID F1 are vendor-specific storage technologies. ZFS is a file system and storage-management platform, while RAID-Z is a parity layout used within ZFS. These options cannot be selected when creating a UGOS Pro storage pool.

Can You Change the RAID Type Later?

UGOS Pro supports the following upward migration path:

Basic → RAID 1 → RAID 5

Starting with one drive in Basic mode:

1. Add a second drive to migrate from Basic to RAID 1.
2. Add a third drive to migrate from RAID 1 to RAID 5.

Moving from Basic to RAID 5 therefore requires two additional drives and follows those stages. JBOD and RAID 0 cannot be migrated to RAID 5, and RAID 5 cannot be downgraded to RAID 1.

Migration is a long, storage-intensive operation. Keep a verified backup before starting, use compatible drives with sufficient capacity, maintain stable power, and avoid heavy workloads until the process has finished.

For help deciding whether to migrate or create a different pool, see our guide to choosing the RAID level for a home NAS.

How Do You Keep a RAID Array Healthy?

RAID protection depends on the remaining drives being readable when a member fails. Set up these controls before the array becomes degraded:

1. Enable notifications. Turn on drive-health, storage-pool, and system alerts so a failed member does not remain unnoticed.
2. Run SMART tests. Schedule short and extended tests, then investigate reallocated sectors, pending sectors, read failures, and other new warnings.
3. Run periodic data scrubbing. On storage pools where UGOS Pro provides the function, scrubbing checks stored data and parity so latent problems can be discovered before a rebuild depends on those blocks.
4. Prepare a compatible replacement. When downtime matters, keep a replacement drive of sufficient capacity available. Check the exact drive in the UGREEN NAS compatibility list.
5. Protect the NAS from interrupted power. A compatible UPS gives the NAS time to finish active writes and shut down cleanly. Our NAS power-outage protection guide explains how communication and controlled shutdown affect that protection.
6. Reduce activity during rebuilding. Pause intensive backups, indexing, media processing, virtual machines, and containers while the array is degraded.
7. Act on a stalled rebuild. Use the RAID rebuild troubleshooting guide if the replacement is rejected, synchronization stops, or another drive reports errors.
8. Test the independent backup. Restore sample files periodically. A completed backup job is useful only if the data can be recovered.

RAID Is Not a Backup

RAID 1, RAID 5, RAID 6, and RAID 10 can keep a storage pool available after specified drive failures. They cannot recover a file deleted by a user, overwritten by an application, encrypted by ransomware, or lost when the entire NAS is stolen or damaged.

The Storage Networking Industry Association makes the same distinction in its explanation of storage mirroring: mirroring reduces downtime after hardware failure, but it does not protect data that is compromised, deleted, or overwritten.

For irreplaceable files:

1. Keep the working copy on the NAS.
2. Maintain another copy on separate storage.
3. Keep one copy at another location or in a properly protected cloud destination.
4. Test that important files can be restored.

If cloud storage is part of that plan, our automated NAS-to-cloud backup guide explains how to separate synchronization from recoverable backup.

RAID determines what happens when a drive fails. Your backup determines whether the data survives everything else.