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RAR / Controllers and hosts / Hyper-V CSV and Storage Spaces Direct

Hyper-V · CSV · VHDX · AVHDX · checkpoints · Storage Spaces Direct · S2D · Detached · event 311 · ReFS · Server 2016 · 2019 · 2022

Hyper-V CSV and Storage Spaces Direct recovery. Cluster volumes on arrays, or slabs across nodes, and the virtual disks inside either.

Hyper-V keeps its virtual machines as VHDX files, with AVHDX files for checkpoints, on NTFS or ReFS volumes: on a single host, a volume on the host's RAID; on a cluster, a cluster shared volume on a shared array or on Storage Spaces Direct, where the nodes' own disks are pooled and slabs mirrored or parity-striped across them. When the array under a CSV fails, the volume goes with it; when Storage Spaces Direct loses more nodes or disks than its resiliency allows, the virtual disk goes Detached or to No redundancy, and Microsoft's troubleshooting page adds that Detached also occurs when the dirty-region tracking log fills, paired with event 311 asking for a data integrity scan. The recovery is four layers again: the array or the pool reassembled from images, the NTFS or ReFS volume opened on the result, each VHDX extracted whole with its checkpoint chain, and the guest's file system opened inside it. A host's array of two to four members is £500 + VAT upwards after the free look, fixed in writing; Storage Spaces Direct and larger sets from £1,250 + VAT.

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.

Models and versions we see.

Which level is it →
Family Models or versions Metadata, defaults and notes
Single hostHyper-V on internal RAIDThe array first; then the volume
Cluster on shared storageCSV on MSA, ME4, VNXThe array's own page; then CSVFS
Storage Spaces DirectServer 2016 onwards; Azure Stack HCIPool database across nodes; slabs by resiliency
CheckpointsAVHDX chainsExtracted in order; merged on copies

What tends to go wrong on Hyper-V.

Four layersThe array or pool from images; the CSVFS volume, NTFS or ReFS, opened read-only on the result; each VHDX extracted with its AVHDX chain; the guest's file system opened inside. A domain controller, an Exchange server and a SQL Server each have their own repair inside their extracted disks.
Checkpoint chainsA virtual machine with checkpoints reads through AVHDX files back to the base VHDX, and a merge interrupted by an array fault leaves the chain half-consolidated. The bench extracts the chain in order and merges on copies, never on the originals.
Storage Spaces Direct and DetachedMicrosoft's troubleshooting page says a virtual disk goes Detached when the dirty-region tracking log is full, and pairs it with event ID 311, virtual disk requires a data integrity scan. The pool database across every node's disks describes the slabs; every node's disks are imaged and the pool reassembled from them.
Repairs across nodesA repair on a degraded S2D pool reads every surviving slab across the cluster. With a node's disks retired and another showing warnings, it is the same second-failure risk as any rebuild, at cluster scale.

Hyper-V CSV and Storage Spaces Direct symptoms, and how long each gives you.

Not listed? Describe it on the form →
Datastore or volume offline; array shows a faultStart with the array. Power down; image the members.Do not delay
Array healthy; datastore inaccessibleThe volume on top. Do not repair it on the originals.Everyday job
Guests corrupt after a rebuild or a cache lossTorn writes inside the virtual disks. Repaired on extracted copies.Everyday job
Cluster lost more nodes than it toleratesEvery affected node's disks. Do not resync.Do not delay
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 the message means on Hyper-V.

Describe yours to us →
What you see The usual reason Where that leaves you
CSV Failed; array shows a faultThe array underneathImage the members; the array first
VM will not start; checkpoint merge failedAVHDX chain half-consolidatedChain extracted and merged on copies
S2D virtual disk Detached; event 311DRT log full, or integrity not assuredDo not reset; read-only attach on images
Array degraded on the host's controllerA member outImage the weak drives before rebuilding
Array failed; datastore or volume goneToo many members outEvery member imaged; the array, then the volume, then the guests
Datastore or CSV inaccessible; array fineThe volume layerA file-system job on the virtual volume
Virtual machine will not startA torn or missing virtual diskExtracted from the volume and repaired

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

Where the controller's metadata survives on the members, the order, stripe size, parity rotation and data offset are read from it. Where it was cleared or overwritten, they are recovered from the data: parity across the members at the same offset should XOR to zero on a consistent stripe, which confirms the level and finds the stale member; where parity lands says the rotation; entropy at stripe edges and the file system's own anchors give the stripe size, the order and the start.

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

From the bench

  • The array or the pool first. Every disk on every affected node imaged before a repair or an integrity scan.
  • Say which virtual machines matter, and which are domain controllers or databases. Their disks are checked inside.
  • Export Get-StorageJob and the cluster log alongside the three Get- outputs; they say what the cluster was doing when it stopped.
  • Four layers: the array, the volume, the virtual disk, the guest. Each is opened in turn on the images, and each is a place a rival's page is silent.
  • Do not let the hypervisor repair anything until the array is imaged. Its repair reads the survivors under load.
  • Say which virtual machines matter. Extraction begins there.

One job, followed all the way through.

UK · RAR-2026-0634JOB LOGGED ✓

A two-node Storage Spaces Direct cluster on Server 2019 that lost a node's motherboard and, during the outage, two disks on the surviving node, leaving the mirror-accelerated parity volume Detached with event 311 and twelve virtual machines on it

Every disk from both nodes came in, labelled by node and slot. The two failed disks were imaged after head swaps; the pool database was read from every image and the newest consistent copy chosen; the virtual disk was assembled from its mirror and parity slabs in software. The ReFS volume was opened read-only, the twelve VHDX files extracted with their checkpoint chains and merged on copies, and each guest's file system checked. The machines went back as exports on fresh media.

100% of the volume recovered14 days here, and back by post
Illustrative example — replace with a genuine case

What helps, and what harms.

Do this much first

  • Export the array log and the hypervisor's view of the storage
  • Power down and label every member by host and slot
  • Send every member of every affected array or disk group
  • Tell us which virtual machines or databases matter most

What sets us back

  • Rebuilding the array with a weak survivor
  • Running the hypervisor's repair or migration on a degraded store
  • Formatting or re-adding a datastore
  • Restoring a backup over the only copy

Questions answered before you commit.

The array under my cluster shared volume failed. Can the virtual machines be recovered?

Usually. The array is reassembled from images, the CSVFS volume opened on the result, each VHDX extracted with its checkpoints, and each guest's file system checked inside.

What does Detached mean on Storage Spaces Direct?

That Windows took the virtual disk offline, and on S2D most often because the dirty-region tracking log filled, with event 311 asking for a data integrity scan. Do not reset the pool; every node's disks are imaged and the pool reassembled.

My checkpoint merge failed and the VM will not start. Is it gone?

No. The AVHDX chain is half-consolidated; it is extracted in order and merged on copies.

What does it cost?

A host's array of two to four members is £500 + VAT upwards after the free look; Storage Spaces Direct and larger sets from £1,250 + VAT, fixed in writing.

Begin here if yours is doing the same thing.

Hyper-V data recovery, the full job →Storage Spaces: no redundancy, detached →Windows Storage Spaces and dynamic disks →VMware VMFS and vSAN →Preserved cache and cache data lost →

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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