Running a NAS, Part 3: Drive Pooling on Windows

A Windows PC pools drives with an add-on or with a Windows feature, and the options guard against different failures. StableBit DrivePool keeps ordinary files on every drive and copies chosen folders to a second one. Microsoft’s Storage Spaces offers mirror and parity layouts. SnapRAID adds snapshot parity beside either, and its author is blunt that only a full backup recovers a disk array that has failed completely.

This is Part 3 of Running a NAS. Part 2, Pools and Filesystems on a NAS, covered how ZFS, Btrfs, Unraid parity, and SnapRAID with mergerfs pool and protect drives. This part covers the Windows answers to the same question, and the pooling tools that have ended. Part 1 compared the systems that run a network-attached storage (NAS)Network-attached storage is a storage system that gives other computers access to its files over a network. box, and a plain Windows PC wasn’t one of them. How other computers then reach a Windows share, and what Windows 11 now demands of an SMB connection, is in Part 6.

The numbers here come from Microsoft’s, StableBit’s and SnapRAID’s own documentation, worded as theirs. The exceptions are the Drive Extender dates, from press reports, and the FlexRAID capture count, from the Internet Archive, and no number here is a test result of mine.

Where Windows pooling came from

Windows once pooled drives by itself. According to ZDNET, Drive Extender in Windows Home Server joined several hard drives into one pool and duplicated data automatically. On November 23, 2010, Microsoft announced it was removing the feature from the coming Windows Home Server code-named Vail, from Small Business Server 2011 Essentials, and from Windows Storage Server 2008 R2 Essentials. Ars Technica reported the reason Microsoft gave as the ready availability of large hard drives.

Pooling tools that ended or went quiet

Drive Bender pooled Windows drives, and it has ended. On April 1, 2023, its maker Division-M announced that Drive Bender was no longer for sale and its development was discontinued. Drive Bender’s change log ends at v3.9.9.5 from August 2, 2022, a release for Windows 11 compatibility.

FlexRAID is harder to date. The Internet Archive holds 229 captures of flexraid.com’s home page between April 2008 and July 2019, and the last one still shows its products and a download button. No statement from the maker about an ending turned up, so this page gives no date for one.

Liquesce, an open-source option

Liquesce is an open-source pooling project on GitHub. Its README describes a tool that merges drives into one view without formatting them. It needs .NET 4.5.1 or newer, plus the Dokan driver for its first phase. Whether anyone still maintains it, the README doesn’t say.

DrivePool leaves your files alone

StableBit DrivePool merges drives into one pool, and the files inside stay ordinary. Its manual says it always stores files in plain NTFS or ReFS format with nothing special added, so another computer that can read those file systems can read the files for recovery. Each file lives in a hidden folder on the drive DrivePool chose for it. Over those per-drive folders, the pool is only a layer and holds no file format of its own.

Adding a drive that is already formatted leaves its contents unchanged. DrivePool takes NTFS and ReFS drives only. It doesn’t support FAT32 or exFAT, and one pool can’t mix NTFS and ReFS. Only simple volumes can join a pool, so dynamic volumes can’t take part.

Placement is simple. By default, DrivePool puts each new file on the pooled disk with the most free space, and its balancing plug-ins change that. Its SSD Optimizer sends all new files to disks marked as SSD and moves them to the archive disks in the background, which makes flash a landing zone for writes. Pools can also nest. DrivePool can add one pool to another, and the child pool keeps its own duplication and balancing settings.

Protection comes from keeping extra copies of files, so it costs disk space for every file it covers.

Duplication and drive failure

DrivePool’s file protection is duplication, and the settings decide how many copies exist and where.

Copies per folder

A file in a duplicated folder exists on at least two physical drives, so one drive can fail and the other copy stays safe. Duplication can cover the whole pool or any single folder, and a folder’s setting can override the pool’s. DrivePool labels the level x2 for two copies of each file, x3 for three, and so on. Normal duplication survives one drive failing at a time, and an option keeps more copies at the cost of more disk space per file.

New files are written to all their copies together by default. With real-time duplication switched off, the performance options have the pool write a single copy first and duplicate in the background. Background duplication never locks files, and it resumes on its own after a reboot.

Reads can use the copies too. DrivePool can read a duplicated file from more than one drive at once for better performance. Reads on duplicated files have had a bug, too. According to its change log, under certain conditions, buffered synchronous reads with no offset could sometimes return incorrect data. The log lists the fix, so anyone on an older build has a reason to update.

When a drive goes missing

Unplug a pooled drive or lose its cable and the pool denies writes until the drive is reconnected or removed. Duplicated files stay fully readable. Files that were not duplicated and lived on that drive are missing from the pool until it returns. After a reconnect, DrivePool runs a full duplication check over the whole pool.

Removing a drive

When a drive leaves the pool, protected files are rebuilt from their other copies and never copied from the drive being removed, so a damaged drive can’t taint them. If the remaining drives lack the space, the removal stops and the drive stays in the pool.

A dead drive follows the manual’s own steps. Disconnect it and remove it from the pool, and duplicated files begin regenerating in the background. Unduplicated files that were on it no longer show up on the pool. A drive that was only unplugged rejoins automatically when reconnected, unless its PoolPart folder was renamed or deleted.

Scanner and CloudDrive: watching drives and reaching the cloud

StableBit Scanner is sold separately from DrivePool. Its surface scan tries to read every sector, so the whole surface of a drive is confirmed readable, and by default it waits 30 days before it re-checks a sector. Per the maker, a scan of an SSD is read-only and in no way harmful. It also calls the scan and file recovery a best-effort approach, so recovering a damaged file may be partial, full, or none.

Background checks and SMART polling

Scanner runs a read-only CHKDSK pass in the background to look for file system damage. It normally queries SMART data every couple of minutes, and a throttle option exists because those queries can keep drives from idling. When it finds unreadable sectors, the product page says it can name the files they belong to and attempt recovery.

How often to run scans and self-tests, and when to schedule them around scrubs, is in Part 8, Keeping a NAS Healthy.

How Scanner works with the pool

A balancer links Scanner to the pool. DrivePool includes a Scanner balancing plug-in for Scanner 2.2 or newer that moves files off damaged drives and handles temperature control, starting a balancing pass at once when damage turns up. Balancers have a priority order and a higher one overrides a lower one, so Scanner placed above the Duplication Space Optimizer can deny a move onto a drive it flagged as failing. DrivePool also includes Volume Equalization, File Placement Limiter, and Prevent Drive Overfill. The manual says balancing exists mainly so free space spreads in a way that lets duplicated files fit, and calls it a power-user feature with reasonable defaults.

A lost CloudDrive password cannot be recovered

StableBit CloudDrive presents a virtual disk whose data lives at a storage provider the user picks. Its product page lists Amazon S3, Backblaze B2, Cloudflare R2, Wasabi, Dropbox, OneDrive for Business, Google Cloud Storage, Azure, FTP, a file share, and a local disk. CloudDrive can encrypt a drive with AES-256 and a key only the user knows. CloudDrive’s manual, written for an older build, says that if the password is lost, no one at StableBit or at the provider can recover the data. That manual also says to never attach a cloud drive to multiple machines at once. CloudDrive’s download page lists a reliable always-on connection of 25Mbps down as a minimum requirement.

DrivePool’s product page says that together with CloudDrive it can store some or all pooled files in the cloud.

Prices and versions in November 2026

StableBit’s buy pages list a one-machine personal license for each tool: DrivePool, Scanner, and CloudDrive. A DrivePool license doesn’t expire with time, and the page says future version upgrades are included. DrivePool also offers a free, fully functional 30-day trial. Its download page lists Windows 10, Windows 11, and Windows Server 2016 through 2025, on x86, x64, and ARM64 processors. The Scanner and CloudDrive download pages carry the current versions in the table.

Source: StableBit buy and download pages, retrieved November 5, 2026. None of the pages gives a release date.

Storage Spaces on a single PC

Microsoft’s overview describes three resiliency types, which are simple, mirror, and parity. On Windows 10 and 11, the setup in Settings offers Simple, Two-way mirror (the default), Three-way mirror, Parity, and Dual parity. It needs at least two extra drives besides the one Windows runs from, and a storage space can’t host the Windows operating system itself. Plain Storage Spaces focuses on resiliency within a single server or external enclosure, while Storage Spaces Direct spans a cluster.

Source: Microsoft, Storage Spaces in Windows (support page, drive counts for Windows 10 and 11) and Storage Spaces overview (failures survived and overhead).

In Microsoft’s words, mirror spaces give greater throughput and lower access latency than parity. Parity spaces are best for archival data and streaming media, it adds, and suit highly sequential workloads such as archive or backup. They also have lower write performance because of parity calculations, and the pages I read give no figure for that penalty. A simple space protects nothing, since it is built for performance and doesn’t protect files from drive failure.

Two practical notes come from Microsoft’s Storage Spaces in Windows page. After adding a drive to an existing pool, it’s a good idea to run drive-usage optimization so some data moves onto the new drive. And many USB enclosures and hubs make Windows treat drives as ineligible, so an external drive can work normally in File Explorer and still not appear in Storage Spaces. Part 9, NAS Problems Found Too Late, returns to USB-connected disks as a buying trap.

ReFS checksums and a disagreement over them

Whether a storage space catches silent corruption depends on the file system on top of it. Microsoft’s integrity streams page says ReFS always uses checksums for metadata but doesn’t, by default, generate or validate checksums for file data. Integrity streams switch the file-data checksums on. With them on, a ReFS volume on a mirror or parity space attempts to correct corruption from another copy. On a simple space or a bare drive, ReFS returns an error without returning the corrupted data.

Microsoft’s support page makes a shorter statement for client Windows. A mirror space formatted with ReFS has Windows automatically maintain data integrity. The integrity streams page adds a caution. Because integrity streams carry a performance cost, Microsoft recommends leaving them disabled on performance-sensitive systems. Its scrubber runs every four weeks by default and can validate file data only for files with integrity streams enabled. Supported ReFS configurations must use Windows Server Catalog certified hardware.

SnapRAID’s FAQ takes a different line. It says that, in contrast to SnapRAID, unRAID and Windows Storage Spaces lack integrity checks. Part 2 weighs the Unraid half of that claim. Both statements come from sources with a stake in the answer, and they don’t agree. This guide reads the Microsoft pages as describing opt-in checksums on file data, which would make SnapRAID’s sentence true of a default setup and incomplete for a volume where integrity streams are on. Checking the setting on the actual volume settles it faster than either document.

SnapRAID beside a pool

SnapRAID is free software under the GPLv3 license. Its download page listed CLI 15.1, released October 2026, as current, and the Windows installer contains both the command-line tool and the Daemon, which has a web GUI. According to the FAQ, SnapRAID provides a basic virtual views and storage pooling solution but is also compatible with other pooling solutions, and it names DrivePool as the Windows companion.

Part 2 covers how its snapshot parity works with mergerfs on Linux, and the pairing with a Windows pool follows the same rule. SnapRAID’s compare page says parity changes only when you run a sync, which lets you recover files accidentally deleted or modified since the last one. On Windows, a file’s timestamp is only guaranteed to update after the file is closed, so the FAQ advises running sync when no program is using the array.

What a pool does not replace

DrivePool’s duplication keeps extra copies of each file and nothing more. In the older 1.X edition of its manual, the maker says a separate backup, unlike duplication, can protect you from user error such as accidental deletions. The same 1.X page warns that imaging the pool drive will not work, since there is no single physical disk to copy, and points to file-based backup tools. It adds that backing up each pool part backs up every duplicated file twice.

For a backup that survives the PC itself, the cloning and backup guide covers copies and where to keep them, and a later part of this series, Apps and Backing Up the NAS, covers the backup tools, the cloud targets and the locks that stop ransomware deleting a copy.

Choosing between them

This guide reads DrivePool as the easier starting point for a mixed pile of drives on a Windows box. Its files stay ordinary NTFS or ReFS files that another computer can read if the PC dies, and Scanner can steer files off a failing drive before it dies. Storage Spaces asks for more decisions up front, namely the layout, the drive minimums in the table, and a separate choice about ReFS integrity streams. The basis for both readings is the makers’ pages above, not a test of mine.

I used to run DrivePool. My own server runs Unraid now, with dual parity, and Part 2 describes it. It’s a 4U, 24-bay machine full of 20TB hard drives, with six 3.2TB SAS SSDs beside them, and those SSDs are where the series goes next. DrivePool’s SSD Optimizer already treats flash as a landing zone for new files, and the next part, SSDs in a NAS, looks at cache, all-flash pools, and what wear and power loss mean for a drive in a NAS.