StorageSpace - Parity

PatZ1989 · 27 Nov 2012 at 20:17

Intelligent minds of OCUK, lend me your brainz.

I'm confused as to how windows 8 storage space has come to the conclusion that a 5 x 2tb array with parity enabled equals 6TB of usable space, screenshots provided - Can anyone comment?

ecksmen · 27 Nov 2012 at 20:52

You need another drive for parity.

Edit

This isn't RAID - in the traditional sense. You have parity across 3 drives (columns). If you want to use the other two spindles, you will need another drive from my understanding.

Edit 2

User powershell to show the numberofcolumns

Code:

get-virtualdisk | fl

Should see something like this

Code:

PS C:\Users\Administrator> get-virtualdisk | fl


ObjectId                          : {bd94efc7-38bd-11e2-93ed-001a92823421}
PassThroughClass                  :
PassThroughIds                    :
PassThroughNamespace              :
PassThroughServer                 :
UniqueId                          : C7EF94BDBD38E21193ED001A92823421
Access                            : Read/Write
AllocatedSize                     : 858993459200
DetachedReason                    : None
FootprintOnPool                   : 1288490188800
FriendlyName                      : FileShare
HealthStatus                      : Healthy
Interleave                        : 262144
IsDeduplicationEnabled            : False
IsEnclosureAware                  : False
IsManualAttach                    : False
IsSnapshot                        : False
LogicalSectorSize                 : 512
Name                              :
NameFormat                        :
NumberOfAvailableCopies           : 0
NumberOfColumns                   : 3
NumberOfDataCopies                : 1
OperationalStatus                 : OK
OtherOperationalStatusDescription :
OtherUsageDescription             :
ParityLayout                      : Rotated Parity
PhysicalDiskRedundancy            : 1
PhysicalSectorSize                : 4096
ProvisioningType                  : Fixed
RequestNoSinglePointOfFailure     : True
ResiliencySettingName             : Parity
Size                              : 858993459200
UniqueIdFormat                    : Vendor Specific
UniqueIdFormatDescription         :
Usage                             : Other
PSComputerName                    :

I suspect you have 3 columns. Not sure how you expand it, but I have read you may need 6 drives. (above done on S 2012, but I'd expect 8 to be the same).

Raumarik · 27 Nov 2012 at 20:53

Almost looks like it's treating it like RAID 6, so it can survive two drives failing. Very odd, sorry for not having much info - haven't really looked into Storage spaces as I've just opted for RAID 5 via RAID controller (for now..)

Interested to see what others say though, I'd have expected it to be around 7.x TB, even RAID 6 would probably see you in at even less than 6TB so it doesn't quite add up.

Must be a new way of working parity then, time to google for storage space calculators!

ecksmen · 27 Nov 2012 at 21:06

I think you'll need to use powershell to create it with 5 columns.

You can control the number of columns and the stripe interleave when creating a new storage space by using the Windows PowerShell cmdlet New-VirtualDisk with the NumberOfColumns and Interleave parameters.

Each type of storage space has a minimum number of stripe columns which translates to a minimum number of physical disks, given their column-to-disk correlation (below).

http://social.technet.microsoft.com/wiki/contents/articles/11382.storage-spaces-frequently-asked-questions-faq.aspx#What_are_columns_and_how_does_Storage_Spaces_decide_how_many_to_use

PatZ1989 · 27 Nov 2012 at 21:55

is there a simple way to work out what the interleave should be, this is quite manual so I dont want to break it =/

ecksmen · 27 Nov 2012 at 22:27

I'd leave it at 256KB myself - it's the default and MS don't talk about benefits of changing it (performance vs cpu load etc...).

Can you make several drives with different interleave and benchmark? It would also depend on what is going on the drive. The days are gone where I worry about this level of detail.

Summary -

5 columns, 256 interleave.

PatZ1989 · 28 Nov 2012 at 10:08

reading their document on deploying the storage spaces with powershell, interesting stuff - so many variables you ahve to supply when doing it this way though - unraid looking like a nice easy alternative atm

ecksmen · 28 Nov 2012 at 11:38

You don't have to provide all the options. This should work... Change the friendly names to the name of your pools if different and size.

Code:

New-VirtualDisk –StoragePoolFriendlyName “Storage Space” –ResiliencySettingName Parity –Size 10TB –FriendlyName “My Storage” -Numberofcolumns 5