Microsoft Storage Spaces Is Hot Garbage For Parity Storage

I love parity storage. Whether it’s traditional RAID 5/6, erasure coding, raidz/raid2z, whatever. It gives you redundancy on your data without requiring double the drives that mirroring or mirroring+stripping would require.

The drawback is write performance is not as good as mirroring+stripping, but for my purposes (lots of video files, cold storage, etc.) parity is perfect.

In my primary storage array, I use double redundancy on my parity, so effectively N+2. I can lose any 2 drives without losing any data.

I had a simple Storage Spaces mirror on my Windows 10 Pro desktop which consisted of (2) 5 TB drives using ReFS. This had four problems:

  • It was getting close to full
  • The drives were getting old
  • ReFS isn’t support anymore on Windows 10 Pro (need Windows 10 Workstation)
  • Dropbox (which I use extensively) is dropping support for ReFS-based file systems.

ReFS had some nice features such as checksumming (though for data checksumming, you had to turn it on), but given the type of data I store on it, the checksumming isn’t that important (longer-lived data is stored either on Dropbox and/or my ZFS array). I do require Dropbox, so back to NTFS it is.

I deal with a lot of large files (video, cold-storage VM virtual disks, ISOs, etc.) and parity storage is great for that. For boot volumes, OS, applications, and other latency-sensitive operations, it’s SSD or NVMe all the way. But the bulk of my storage requirements is, well, bulk storage.

I had a few more drives from the Best Buy Easystore sales (8 TB drive, related to the WD Reds, for about $129 during their most recent sale) so I decided to use three of them and create myself a RAID 5 array (I know there are objections to RAID 5 these days in favor of RAID 6, while I agree with some of them, they’re not applicable to this workload, so RAID 5 is fine).

So I’ve got 3 WD Easystore shucked drives. Cool. I’ll create a RAID 5 array.


Shit. Notice how the RAID-5 section is grayed out? Yeah, somewhere along the line Windows removed the ability to create RAID 5 volumes in their non-server operating systems. Instead Microsoft’s solution is to use the newer Storage Spaces. OK, fine. I’ll use storage spaces. There’s a parity option, so like RAID 5, I can do N+1 (or like RAID 6, N+2, etc.).

I set up a parity storage space (the UI is pretty easy) and gave it a quick test. At first, it started sending at 270 MB/s, then it dropped off a cliff to… 32 MB/s.



That’s it. 32 MB/s a second. What. The. Eff. I’ve got SD cards that can write faster. My guess is that some OS caching was allowing it to copy at 270 MB/s (the hard drives aren’t capable of 270 MB/s). But the hard drives ARE capable of far more than 32 MB/s. Tom’s Hardware found the Reds capable of 200 MB/s sequential writes. I was able to get 180 MB/s with some file copies on a raw NTFS formatted drive, which is inline with Tom’s Hardware’s conclusion.

Now, I don’t need a whole lot of write performance for this volume. And I pretty much only need it for occasional sequential reads and writes. But 32 MB/s is not enough.

I know what some of you are thinking. “Well Duh, RAID 5/parity is slower for writes because of the XOR calculations”.

I know from experience on similar (and probably slower) drives, that RAID 5 is not that slow, even on spinning disks. The XOR calculations are barely a blip in the processor for even halfway modern systems. I’ve got a Linux MD RAID system, with 5 drives and I can get ~400 MB/s of writes (from a simple dd write test).

While it’s true RAID 5 writes are slower than say, RAID 10, they’re not that slow. I set up a RAID 5 array on a Windows Server 2016 machine (more on that later) using the exact same drives it was able to push 113 MB/s.


It might have been able to do more, but it was limited by the bottleneck of the Ethernet connection (about 125 MB/s) and the built-in Dell NIC. I didn’t have an SSD to install Windows Server 2016 on and had to a use a HDD that was slower than the drives the RAID 5 array was built with so that’s the best I could do. Still, even if that was the maximum, I’ll be perfectly happy with 113 MB/s for sequential writes.

So here’s where I got crafty. The reason I had a Windows 2016 server was that I thought if I created a RAID 5 volume in Windows 2016 (which you can) I could simply import the volume into Windows 10 Pro.

Unfortunately, after a few attempts, I determined that that won’t work.


The volume shows failed and the individual drives show failed as well.

So now I’m stuck with a couple of options:

  • Fake RAID
  • Drive mirroring
  • Parity but suck it up and deal with 32 MB/s
  • Parity and buy a pair of small SSDs to act as cache to speed up writes
  • By a Hardware RAID Card

Fake Hardware RAID

Early on in my IT career, I’d been fooled by fake RAID. Fake RAID is the feature that many motherboards and inexpensive SATA cards offer: You can setup RAID (0, 1, 5 typically) in the motherboard BIOS.

But here’s the thing: It’s not a dedicated RAID card. The RAID operations are done by the general CPU. It has all the disadvantages of hardware RAID (difficult to troubleshoot, more fragile configurations, very difficult to migrate) and none of the advantages (hardware RAID offloads operations to a dedicated CPU on the RAID card, which fake RAID doesn’t have).

For me, it’s more important to have portability of the drives (just pull disks out of one system and into another). So fake RAID is out.

Drive Mirroring

Having tested drive mirroring performance, it’s definitely a better performing option.

Parity with Sucky Performance

I could just suck it up and deal with 32 MB/s. But I’m not going to. I don’t need SSD/NVMe speeds, but I need something faster than 32 MB/s. I’m often dealing with multi-gigabit files, and 32 MB/s is a significant hindrance to that.

Parity with SSD Cache

About $50 would get me two 120 GB SSDs. As long as I wasn’t doing a massive copy beyond 120 GBs of data, I should get great performance. For my given workload of bulk storage (infrequent reads/writes, mostly sequential in nature) this should be fine. The initial copy of my old mirrored array is going to take a while, but that’s OK.

The trick with an SSD cache is that you have to use PowerShell in order to configure it. The Windows 10 GUI doesn’t allow it.

After some fiddling, I was able to get a Storage Space going with SSD cache.

And… the performance was worse than with the drives by itself. Testing the drives by themselves, I found the that the SSDs had worse sequential performance than the spinning rust. I’d assumed the SSDs would do better, a silly assumption now that I think about it. At least I’m out only $50, and I can probably re-purpose them for something else.

The performance for random I/O is probably better, but that’s not what my workload is on these drives. My primary need is sequential performance for this volume.

Buy A Hardware RAID Card

I don’t like hardware RAID cards. They’re expensive, the software to manage them tends to be really awful, and it make portability of drives a problem. With software RAID, I can pull drives out of one system and put them into another, and voila, the volume is there. That can be done with a hardware RAID card, but it’s trickier.

The performance benefit that they provide is just about gone too, given how fast modern CPUs are and how many cores they have, compared to the relatively slow CPUs on hardware RAID cards (typically less than a GHz, and only one or two cores).


So in the end, I’m going with a mirrored pair of 8 TB drives, and I have two more drives I can add when I want to bring the volume to 16 TB.

Thoughts On Why Storage Spaces Parity Is Such Hot Fucking Garbage

There’s a pervasive thought in IT that parity storage is very slow unless you have a dedicated RAID card. While probably true at one time, much like the jumbo frame myth, it’s no longer true anymore. A halfway modern CPU is capable of dozens of Gigabytes per second of RAID 5/6 or whatever parity/erasure coding. If you’re just doing a couple hundred megabytes per second, it’s barely a blip in the CPUs.

It’s the reason huge honking storage arrays (EMC, Dell, NetApp, VMware VSAN etc.) don’t do RAID cards. They just (for the most part) throw x86 cores at it through either scale-up or scale-out controllers.

So why does Storage Space parity suck so bad? I’m not sure. It’s got to be an implementation problem. It’s definitely not a CPU bottleneck. It’s a shame too, because it’s very easy to manage and more flexible than traditional software RAID.


Tried parity in storage spaces. It sucked bigtime. Tried other shit, didn’t work. Just went with mirrored.

17 Responses to Microsoft Storage Spaces Is Hot Garbage For Parity Storage

  1. Markus says:

    Because of all that described mess, I use drivepool. Standard based, reliable, gets the job done, inexpensive

  2. Markus Schloesser says:

    Because of all that described mess, I use drivepool. Standard based, reliable, gets the job done, inexpensive

  3. J-Dub says:

    While I agree that parity based storage spaces blow i think i have some light to shed on your SSD caching issue. In my experience the SSD caching works pretty well with enterprise SSDs, more specifically SSDs power loss protection (PLP).

    What you are running into is likely because you used consumer SSDs ($50 for 2x drives?) which pretty much never have power loss protection.

    Most consumer and enterprise drives use a fast DRAM or SLC Flash cache to absorb writes and then dole them out to the slower MLC or QLC flash. The difference is the PLP. Enterprise drives include capacitors on board to ensure that during a power loss event that the DRAM or SLC cache has time to flush to the primary storage before the drive runs out of power.

    In your typical windows environment these SSDs are treated the same. However in Storage Spaces the caching mechanism requires a “verified write”, drives without PLP are not considered to have a “verified write” until the SSD cache has fully written to the drive, basically ignoring the fact that you wrote to the fast DRAM or SLC cache and waiting for the drive to write to the MLC or QLC. Often times bypassing the cache on a value branded consumer drive yields pretty pitiful results as the MLC or QLC struggles to maintain even spinning rust levels of I/O.

    The OS can identify drives with PLP based on their S.M.A.R.T. data and will let the drives use their caching devices as a verified write allowing you to see the expected increase in speeds you’d expect from using SSDs.

    I can say from first hand experience that in a 2x drive SSD cache mirror that 2x 480gb Intel S3710’s trounce 2x technically faster 500gb Samsung 850 EVO drives.

  4. Datacenter Underlord says:

    I am guessing you have never had a decent HW RAID card.
    I got a 3ware card back in 2008 or so, I think it was the 9650 – it could write 550Mbytes/second on an 8x320Gbyte RAID 6 setup – needless to say, locally, because there was no network that could handle that load at the time.
    I got an Adaptec 51645 a couple of years later. It is much, much slower, writes only 200Mbytes/s in the same system, locally (8x4Tbyte RAID 6). But, I don’t mind because it still saturates the gigabit LAN cards at about 110MBytes/s, so it feels pretty snappy anyway.
    The best thing about this Adaptec card is the ability to power down individual disk – with the 3ware card could not do. Albeit, the 3ware card was a performance card. I ended up keeping the Adaptec card because it extends the lifetime of disks.
    Both cards ran in the same system: a Zotac 9600 ITX board with a cheap 800MHz processor, 512 MB RAM, Ubuntu. It was headless, system, collecting dust in the corner. Still runs.

  5. Datacenter Underlord says:

    Sorry, a typo there. Zotac 9300, not 9600 😉

  6. Krautmaster says:

    i just created the volume with the params -Interleave 128KB -WriteCacheSize 0GB so actually disabled the cache on parity and i get at least ~100-140 MB/s constant write (a 300% uplift from MS standard). Lets see of i can further improve

    Edit: howly cow. Seems like i found the secret sauce in Storage Spaces Parity. Smaller -Interleave values together with disabled cache bumbs ur transfers wen further. With -64k im >150MB/s on a 4 column Parity with 4×12 TB drives. Its not brilliant but better than 30-35Mb/s.

    And you really have to set NumberOfColumns to the amount of Drives in ur parity, else MS does any weird mess.

  7. Krautmaster says:

    check out my last post here:

    Edit: howly cow. Seems like i found the secret sauce in Storage Spaces Parity. Smaller -Interleave values together with disabled cache bumbs ur transfers wen further. With -64k im >150MB/s on a 4 column Parity with 4×12 TB drives. Its not brilliant but better than 30-35Mb/s.

    And you really have to set NumberOfColumns to the amount of Drives in ur parity, else MS does any weird mess.

    Summary of my cmdlets to create an ReFS Tier with SSD + HDD = Mirror and a Second one with SSDs = Mirror and HDD = Parity, optimized for Parity Speed.

    New-StoragePool -FriendlyName “Poolname” -StorageSubsystemFriendlyName “Windows Storage*” -PhysicalDisks $PhysicalDisks -ResiliencySettingNameDefault Parity

    New-StorageTier -StoragePoolFriendlyName “Poolname” -FriendlyName SSD_Tier -MediaType SSD

    New-StorageTier -StoragePoolFriendlyName “Poolname” -FriendlyName HDD_Tier -MediaType HDD

    New-Volume -FriendlyName “SSD_HDD_Tier_Mirror” -FileSystem ReFS -StoragePoolFriendlyName “Poolname” -StorageTierFriendlyNames SSD_Tier, HDD_Tier -StorageTierSizes 100GB, 4000GB -ResiliencySettingName “Mirror”

    Remove-StorageTier -FriendlyName SSD_Tier
    Remove-StorageTier -FriendlyName HDD_Tier

    New-StorageTier -StoragePoolFriendlyName “Poolname” -FriendlyName HDD_Tier_Parity -MediaType HDD -ResiliencySetting Parity

    New-StorageTier -StoragePoolFriendlyName “Poolname” -FriendlyName SSD_Tier_Mirror -MediaType SSD -ResiliencySetting Mirror

    Set-StorageTier -FriednlyName “HDD_Tier_Parity” -NumberOfColumns 4 -Interleave 64KB

    New-Volume -FriendlyName “SSD_HDD_Tier_Parity” -FileSystem ReFS -StoragePoolFriendlyName “Poolname” -StorageTierFriendlyNames SSD_Tier_Mirror, HDD_Tier_Parity -StorageTierSizes 120GB, 27510GB -WriteCacheSize 0GB

    Remove-StorageTier -FriendlyName SSD_Tier_Mirror
    Remove-StorageTier -FriendlyName HDD_Tier_Parity

    Get-StorageTier | FT FriendlyName, ResiliencySettingName, PhysicalDiskRedundancy, FaultDomainAwareness, NumberOfDataCopiesget
    Get-VirtualDisk | Select-Object FriendlyName,HealthStatus, OperationalStatus, DetachedReason

    would be nice if someone tries out 😉

  8. RM says:

    Are you sure those Easystore drives weren’t SMR?

  9. Kayden L Fox says:

    You’re not alone. Parity spaces are total shit after 1607.

    W10-1607 Everything fine. 1703 and newer, starting VMs kills parity storage space.
    I had 8 2tb disks in a parity space on 1607 and everything was great.

    Windows update forced 1703 on me and things broke. When starting the VMs, they sit at a black screen with the space at 100% activity moving 0 data until the storage space goes offline due to critical write failure. If I try to power off the VMs, they just sit there “Stopping” until the space goes offline. Even rebooting the host just sits there until the space comes offline. I rolled back to 1607 and disabled updates.

    Forward a few months and my system updates itself to 1803 and the issue comes back, only I can’t go back to 1607 and reinstalling the host every few months doesn’t seem like a good plan.

    All disks are fine individually and show no issues. Only error in event viewer is that the pool went offline. It comes right back online and all the data works fine until you try to start VMs again.

    I changed the hyper-v scheduler type, disable hyper threadding, killed C states, set VMs to a single core, disabled dynamic RAM, and a dozen other things.

    It just seems like VMs+ parity spaces are totally broken. I created a mirror pool and while they run like garbage, they did boot. Being the disks were from 2010, I thought it might just be time to replace them. I used diskspeed to bench the disks solo and every one of them out performed the parity pool of 7 other disks… which simply shouldn’t happen with read tests.

    Despite it not seeming like the disks, I went from 7.2k 2TB 32mb cache 3gbps disks to 7.2k 4tb 256mb cache 6gbps disks and not a damn thing changed. Starting 2 single core VMs with 2048mb of ram takes down my parity space of locking up for 20 minutes.

    Also, contacting microsoft support only results in losing 4 hours of your life for them to go “oh, it’s a vm, give us $500.” I cannot adequately convey my rage at the gross incompetence of microsoft’s support and I just wish there was more I could do than whine about it on Reddit. It’s absolute garbage.

  10. snoozeroo says:

    The title of the article summarizes the problem perfectly.

  11. teemsan says:

    Your parity storage space results seem on par with many others reporting the same crap speeds.

    I have seen one workaround if your system is connected to a UPS and your willing to take the risk. Go to Device Manager >Disk Drives > Disks x (whatever your storage space disks are) >Properties >Policies and selecting “Turn off write-cache buffer flushing on this device”

    But if your device ever does suffer a hard off pwr failure you risk losing everything and corrupting the drive.

    The “Turn off write-cache buffer …” advice and variations of PowerShell tweaks (depends on your system and setup) are in several forum threads to overcome the painfully slow speeds. Mileage varies.

    I’m about to set up and test this myself on a parity storage space 4 x 4TB drives

  12. John Griffin says:

    I have exactly the same issue. I upgraded my “Home Server” and upgraded from 2012R2 to server 2019. I pulled the same 4x4TB drives over, and thought that i’d upgrade from RAID 5 to SS with parity. I noticed immediately that the performance was in the toilet despite 6 years newer hardware (apart from the drives).

    Result? Well all the below is copying a 100GB from local SSD. I wait about 2 minutes as it seems to scream for about 20 seconds then fall off a cliff. I believe there is something wrong with Microsoft’s code

    1. Storage Spaces 4x Drive with Parity. – 13MB/s
    2. RAID 5 4x drive with parity – 23MB/s
    3. Running Linux under Hyper-V, RAID 5, copied over CIFS: – 230MB/s
    4. RAID 0 4x drive stripe – 420MB/s

    All on the same server, same hardware etc. The fact that running RAID 5 under a VM is 10x – 20x faster points to something seriously wrong with MS’s code.

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  15. Adam Korman says:

    There is a solution to this problem – With 3 nearline drives I can get 200+ MB/s on parity storage spaces.

    The solution is actually so simple I consider it a critical failing that Microsoft didn’t make it a default. It is… format the volume to use the same cluster size as the stripe size (“interleave”) in the array. The default is 256 KB, but if you use powershell you can make the interleave smaller so you can use smaller clusters. I have mine set to 64K. My write speed went from 20 MB/s to bouncing between 100 and 250. That’s still not the theoretical max one may see with He6 drives in RAID 5, which would be 350 for fully sequential writes, but it’s not bad.

    Larger cluster/interleave sizes like the default 256K will probably lead to slightly increased performance at the expense of wasting capacity with smaller files, but if it is all video files, this is a non-issue.

    I also have Windows cache buffer flushing disabled and am doubling up on write caching by also enabling it in AMD RAID (although I’m not using it for RAID since they axed RAID 5 on non-threadripper CPUs).

    My next experiment is to add a fourth drive and optimize to see if I get some boosted performance.

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