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RAR / Every level and layout / Storage Spaces parity and mirror

Storage Spaces · parity · two-way mirror · columns · slabs · No redundancy · Detached · ReFS · KB4568129

Storage Spaces parity and mirror recovery. Slabs allocated across columns, a pool database that describes them, and states Microsoft names but does not explain.

Windows Storage Spaces is software RAID that does not call itself RAID. A pool of physical disks is carved into slabs, and a virtual disk, mirror or parity, is allocated slab by slab across a number of columns, with the map kept in a pool database replicated on the disks. A two-way mirror tolerates one disk, a three-way mirror two, a parity space one, dual parity two. It fails in the ways the map allows: too many disks lost, which Microsoft's documentation calls No redundancy, a virtual disk taken offline as Detached, one without enough redundancy left to repair as Incomplete, and a pool whose database disagrees with itself after an update or a power event. In 2020 a Windows 10 2004 update left parity spaces showing as RAW until KB4568831 fixed it, and Microsoft's own advice was not to run chkdsk. A set of two to four physical disks is £500 + VAT upwards after the free look, fixed in writing, 5–10 days at the bench.

Free first lookOne fixed figure in writingNo data, no bill on most jobsReturn postage paid

Rather talk it through? An engineer answers the bench line
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Power down. Label every slot before a drive comes out. Do not rebuild, do not force a drive online, do not import or clear a foreign configuration, do not initialise, and do not run chkdsk, fsck, zpool import -F or mdadm --create on the members. A rebuild reads every sector of every survivor and writes to the replacement; each of the commands writes to the drives. On images, all of them are reversible. On the originals, none of them is.

Storage Spaces symptoms, and what each means.

Not listed? Describe it on the form →
Warning: Unhealthy; one disk missingStill readable. Image the missing disk before it is replaced.Do not delay
No redundancyMicrosoft: the virtual disk has lost data because too many drives failed. Power down; image all.Do not delay
Detached (by policy)Taken offline, or requiring manual attach. Usually recoverable; do not reset the pool.Everyday job
IncompleteNot enough redundancy left to repair. Image before any repair.Do not delay
Volume shows RAW after a Windows updateThe 2020 parity issue, or a pool metadata fault. Do not run chkdsk.Do not delay
Pool read-only after an upgradeMetadata version mismatch. Do not delete or recreate.Everyday job
Packing it and posting it: power down, photograph the controller's screen or export its log, and write the slot number on each drive with a marker before it comes out of its carrier. Send every member of the set, including the one that failed first; it holds the stripes the rebuild never reached. Each drive travels in an anti-static bag inside its own padding, in a box with nothing able to move. Send the controller if it was replaced or holds an encryption key; otherwise it stays. Insure the parcel for what the data is worth, use a tracked service, and know that the posting address is not printed anywhere on this site; it arrives by email in reply to the form, with a booking sheet to print; the sheet inside the parcel is what matches it to your enquiry when it is opened. Or hand the sealed parcel in at the nearest of ten drop-off points, your name on the outside and the sheet inside; say where you are on the form and it comes by email. We pay the postage home either way. The whole of it is written up on the guide to packing and posting.

What it tolerates, what fails it, and what the bench has to find.

Columns and interleaveA parity space with three columns and a 256KB interleave writes 256KB to each of two disks and parity to the third, then rotates. A mirror with one column writes each slab to two disks. The number of columns and the interleave are set at creation and recorded in the pool database, and a reconstruction reads them from there.
The pool databaseEvery physical disk carries a copy of the pool's metadata, describing the pool, its virtual disks and the slab map. When copies disagree after a power event or a failed update, Windows takes the virtual disk offline. The bench reads every copy and uses the newest consistent one.
The 2020 parity issueMicrosoft's KB4568129 documented parity Storage Spaces showing as RAW after the Windows 10 and Server 2004 update, with a compatibility hold from 19 June 2020 and a fix in KB4568831 on 31 July. Microsoft's guidance while it lasted was not to run chkdsk.
Storage Spaces DirectThe same slabs across a cluster, with Detached meaning the dirty-region tracking log filled and event 311 asking for an integrity scan. The nodes' disks are imaged and the pool reassembled from them, on the hosts page.

What a reconstruction has to determine.

Describe yours to us →
Unknown Where it is read from What goes wrong when it is guessed
Column count and interleaveThe pool database on each diskData and parity read from the wrong disks
Slab mapThe pool databaseSlabs assembled in the wrong order
Current database copySequence numbers across the copiesAn old map applied to new data
File systemNTFS or ReFS structures on the virtual diskRepairs written to the originals

From the parcel arriving to your files going back.

Work we have closed →
01

Logged the day it lands, and the first look costs nothing Free

A case number goes on the parcel and a number on every member the day it is opened, matched to the slot you wrote on it. Each member goes on the imager its interface needs, never on a controller, and its metadata is read before a sector is: the level, the order, the stripe size, the event counts that say which member is current and which dropped out first. An engineer settles what has happened to the set and how much of it can honestly be read back. Back to you come two things together: a straight note of what is liftable and what is not, plus one figure, fixed and written down. Accept it, or decline and owe us nothing.

Nothing to pay for lookingA single figure, put in writingNo rebuilds, no imports, no initialise
02

Every member imaged, including the one that failed first

Every drive in the set is imaged sector by sector, weak areas last, on hardware that controls every retry, with a map of what could not be read kept for each. Members with failed heads go to the clean bench first; that is the drive site's work and the same bench does it. The drive that dropped out first is imaged too, because it still holds every stripe written before it dropped, and a rebuild that stalled part-way never reached them.

Sector by sector, weak areas lastThe first-dropped member included
03

The geometry, from the metadata or from the parity

A Storage Spaces pool is read from images of every physical disk: the pool database from each, the newest consistent copy chosen, the virtual disk's columns, interleave and slab map taken from it, and the virtual disk assembled from the slabs in software. NTFS or ReFS is opened read-only on the result.

Metadata first, parity secondOrder, stripe, rotation, offset
04

Assembled in software, and repaired on the virtual volume

The set is put together from the images in software, with nothing written to any of them: the current members in, the stale member used only to fill holes a survivor could not give. The file system is checked and repaired on a copy of the virtual volume, VMFS and CSV volumes opened and the virtual machines' disks extracted, databases repaired where they need it. The originals are not touched again.

Nothing written to the imagesVirtual machines and databases opened
05

You see the file list before you pay

What was recovered is listed for you first, and only then does a bill exist. Approve the list and it is invoiced; turn it down and it is not — and where nothing has come back, most jobs carry no charge at all. Recovered data travels home on fresh media bought in for your job, with the postage at our end. Your case is not closed until you have opened the files on a machine of your own.

No charge until you accept the figureFresh media, supplied with the job5–10 days at the bench

What arrives most often

  • Do not run chkdsk on a space that shows RAW. Microsoft said so in 2020, and it holds for every case where the map, not the volume, is the fault.
  • Do not reset or delete the pool. Windows offers it as a way to recover the disks for reuse; the database is what you need.
  • Send every physical disk, including the one Windows says is missing. The slab map spans them all.
  • Say the Windows version and the update history. Pool metadata versions changed across releases, and the tools follow.

One job, followed all the way through.

UK · RAR-2026-0609JOB LOGGED ✓

A four-disk parity space on Windows Server 2019 holding a firm's file shares, one disk failed, a second retired by Windows during the repair, and the virtual disk reported as No redundancy

All four disks came in. The two retired disks were imaged, one with its weak areas last; the pool database was read from every image and the newest consistent copy chosen. The virtual disk's three columns and 256KB interleave came from it, the slab map likewise, and the virtual disk was assembled from the slabs in software with the first-retired disk's slabs filling what the second could not read. The ReFS volume was opened read-only and the shares copied out.

99.99% of the volume recovered8 days here, and back by post
Illustrative example — replace with a genuine case

What helps, and what harms.

Do this much first

  • Power down and note which disk Windows retired first
  • Send every physical disk in the pool
  • Export Get-StoragePool, Get-VirtualDisk and Get-PhysicalDisk output
  • Say the Windows version and recent updates

What sets us back

  • Running chkdsk on a RAW space
  • Resetting or deleting the pool
  • Repairing with a disk showing warnings
  • Removing the missing disk from the pool

Questions answered before you commit.

My Storage Space says No redundancy. Is the data lost?

Microsoft's documentation says it has lost data because too many drives failed. In practice the drives are usually imageable, and the virtual disk is assembled from images with the slab map. Power down and send every disk.

Should I run chkdsk on the RAW volume?

No. Where the pool's map is the fault, chkdsk repairs a volume that is not there and writes the damage back. Microsoft's own guidance in 2020 was not to.

What does Detached mean?

That Windows took the virtual disk offline, by policy or because its integrity could not be assured. It is usually recoverable; do not reset the pool.

What does it cost?

£500 + VAT upwards for two to four disks after the free look, fixed in writing; larger pools and Storage Spaces Direct from £1,250 + VAT.

How long does it take?

5–10 days at the bench.

Begin here if yours is doing the same thing.

Storage Spaces: no redundancy, detached →Windows Storage Spaces and dynamic disks →Hyper-V CSV and Storage Spaces Direct →JBOD, spanned and dynamic disks →

Nothing gets worse while it is powered down.

Looking at it is free. Back comes a list of what opened and what did not, together with a single price to finish, set down in writing while you are still free to say no. On most jobs an invoice only follows the data. Until that list reaches you, leave the server off and the drives in their slots.

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Price my jobPacking and posting