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RAR / Every level and layout / SHR and Synology RAID F1

SHR · SHR-2 · md2 · md3 · LVM · vg1 · System Partition Failed · RAID F1 · Btrfs on top

SHR and RAID F1: the array layer. Ordinary mdadm arrays across partitions of different sizes, glued together by LVM, under a Btrfs or ext4 volume.

Synology Hybrid RAID is not a new arithmetic. On the drives it is Linux mdadm: every drive is partitioned into a small RAID 1 system partition, a swap partition and one or more data partitions, and SHR builds a RAID 5 or 6 across the largest partition every drive shares, then a further RAID 5 across the extra space the larger drives have, and joins the resulting md devices into one LVM volume group with the Btrfs or ext4 volume on top. SHR-2 does the same with two parities. RAID F1 is Synology's all-flash variant, a RAID 5 with parity placed unevenly so that the SSDs do not wear out together. This page is about that layering, and about reassembling it from images of the members; the unit itself, its dashboard and what its Repair button does are on the NAS site. A set of two to four members 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.

SHR symptoms, and what each means.

Not listed? Describe it on the form →
Storage pool DegradedA member lost; still readable. Image before Repair.Do not delay
Storage pool CrashedPast the parity. Synology says you can no longer repair it yourself. Power down.Do not delay
System Partition FailedThe small RAID 1 across every drive has lost a member. Often not the data.Everyday job
Volume crashed; pool healthyThe Btrfs or ext4 on top. A file-system job on the images.Everyday job
Repair started and stalledA survivor's read errors. Power down.Do not delay
Drives moved to another unit; pool not recognisedOrder or DSM version. Do not create a new pool.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 it tolerates, what fails it, and what the bench has to find.

Three layers, or fourmd arrays across partitions, LVM across the md devices, and the file system across the logical volume, with Btrfs snapshots inside that. Each layer is assembled from images in turn, and each has its own way of going wrong.
Mixed sizesTwo 4TB and two 8TB drives in SHR give a RAID 5 across four 4TB partitions and a RAID 1 across the two extra 4TB halves, joined by LVM. The extra arrays have different member counts, and a reconstruction has to find each one's geometry separately.
System Partition FailedThe 2GB RAID 1 that holds DSM is across every drive; when one drive drops out of it the dashboard says the system partition failed, which sounds worse than it is. The data arrays are separate, and often fine.
RAID F1Synology's all-flash layout puts more parity on one drive so that the SSDs do not reach their wear limit together. It is a RAID 5 with an uneven parity map, recorded in the metadata and read from it.

What a reconstruction has to determine.

Describe yours to us →
Unknown Where it is read from What goes wrong when it is guessed
md order, chunk and layoutThe mdadm superblock (1.2) on each partitionA wrong layout on one md device corrupts one segment of the volume
LVM segmentsThe volume group's metadata on the md devicesSegments joined in the wrong order
Newest membersEvent counts in each superblockA stale member assembled in
File systemBtrfs superblocks; ext4 superblock and backupsRepairs 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

An SHR set is assembled layer by layer from the images: each md array from its superblocks, with event counts choosing the current members; the LVM volume group from its metadata across the md devices; and the Btrfs or ext4 volume opened read-only on the result, with snapshots read where they help. Nothing is written to any image.

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 press Repair with a second drive weak. The repair reads every sector of the survivors. The NAS site says why at length.
  • Keep the drives in bay order, and do not move them to another unit to see. DSM's metadata says the order, but a new unit may offer to create a pool.
  • System Partition Failed is usually not the data. It is the small RAID 1 that holds DSM.
  • RAID F1 is a RAID 5 with an uneven parity map. It is read from the metadata, not guessed.

One job, followed all the way through.

UK · RAR-2026-0608JOB LOGGED ✓

A five-bay Synology in SHR-2 with two 8TB and three 4TB drives, two members failed, the pool Crashed, and the owner told by the dashboard that it could no longer be repaired

All five drives came in bay order. The two failed members were imaged, one after a head swap. Three md arrays were found across the partitions: a RAID 6 across five 4TB partitions and two smaller arrays across the 8TB drives' extra space. Each was assembled from the images with event counts choosing the current members, the LVM group joined from them, and the Btrfs volume opened read-only. The shares were copied out.

100% 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 at Crashed, or at Degraded with a second drive warning
  • Number the bays and send every drive
  • Tell us the model, the DSM version and whether SHR-2
  • Say whether Repair was started

What sets us back

  • Pressing Repair with a second drive weak
  • Moving the drives to another unit to see
  • Creating a new pool on the drives
  • Assuming System Partition Failed means the data is gone

Questions answered before you commit.

Is this the page for my Synology?

For the array layer inside it, yes: the md arrays, the LVM group and how they are reassembled from images. For the unit, the dashboard, the Repair button and what each status means, the NAS site covers it in full.

What is SHR underneath?

Linux mdadm arrays across partitions of the drives, joined by LVM, with Btrfs or ext4 on top. Nothing proprietary; the layering is what has to be reassembled.

Can I move SHR drives to another Synology?

Sometimes, in bay order, with a DSM version that supports the pool. If any drive has a fault, the new unit rebuilds into it. Send the set here first.

What does it cost?

£500 + VAT upwards for two to four members after the free look, fixed in writing; larger units from £1,250 + VAT.

How long does it take?

5–10 days at the bench.

Begin here if yours is doing the same thing.

QNAP read-only, Synology crashed →Synology: the array layer →mdadm and LVM →Linux mdadm →

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.

0800 6890668

Price my jobPacking and posting