using all of raid5 disk space W7x64Pro

[Darfyddi]

Hi,

I have 4 HDD which should total 4TB and can not figure out how to use all the space that is available after setting them up in RAID5 form.

I currently have:

100.00MB > System Reserved
2047.90GB > 'C' Drive
746.54GB > Un-allocated

I know that it is not possible to have one C drive of above 2047.90GB but I would like to know how I can partition the 746.54GB as a seperate drive and also why the numbers only add up to about 3TB and not 4TB?

Many thanks for any help.

 

[Golden]

Hi,

In a RAID5 configuration, one of the 4 disks is used as the parity data disk, leaving a total of 3 disks for the total volume available.

From http://en.wikipedia.org/wiki/Standard_RAID_levels

RAID 5 usable size
Parity data uses up the capacity of one drive in the array (this can be seen by comparing it with RAID 4: RAID 5 distributes the parity data across the disks, while RAID 4 centralizes it on one disk, but the amount of parity data is the same). If the drives vary in capacity, the smallest of them sets the limit. Therefore, the usable capacity of a RAID 5 array is

, where N is the total number of drives in the array and Smin is the capacity of the smallest drive in the array.

See this link as to how it works:

RaidCalc - Raid Disk Space Utilization Calculator - Raid, RAID, Redundancy, Performance - iBeast Business Solutions

Regards,
Golden

 

[Darfyddi]

Cheers Golden,

I thought that was the case but am now wondering about the odd 277.46GB missing over the amount of the 1tb disk, seems a huge amount of space; though not as much as the 746.54GB that I can actually see and marked as un-allocated but wont let me touch it

[EDIT]

Sorry, just wanted to say thank you for the link to the RaidCalc site, it showed ~211GB would be used so that might be the 277GB I can't account for.

 

[Golden]

Hi,

The "missing" 277GB is actually used in "creating" the RAID - that is normal, although the actual amount varies a little depending on the disks and RAID controller. See image below.

Can you post a maximised image/screen capture of your Disk management so we can see this unallocated 746GB?

Regards,
Golden

 

[kado897]

Hi,

In a RAID5 configuration, one of the 4 disks is used as the parity data disk, leaving a total of 3 disks for the total volume available.

From Standard RAID levels - Wikipedia, the free encyclopedia

RAID 5 usable size
Parity data uses up the capacity of one drive in the array (this can be seen by comparing it with RAID 4: RAID 5 distributes the parity data across the disks, while RAID 4 centralizes it on one disk, but the amount of parity data is the same). If the drives vary in capacity, the smallest of them sets the limit. Therefore, the usable capacity of a RAID 5 array is

, where N is the total number of drives in the array and Smin is the capacity of the smallest drive in the array.

See this link as to how it works:

RaidCalc - Raid Disk Space Utilization Calculator - Raid, RAID, Redundancy, Performance - iBeast Business Solutions

Regards,
Golden

Just to be clear. It doesn't use a single physical disk for parity. It stripes the data and parity across all four disks so that if one physical disk fails you lose no data.

 

[Golden]

Just to be clear. It doesn't use a single physical disk for parity. It stripes the data and parity across all four disks so that if one physical disk fails you lose no data.

Thanks for clearing that up Kado

 

[kado897]

You are welcome.

 

[Darfyddi]

Thank you as well Kodo, that info' along with that about the raid itself taking up space helps alot.

Here is a pic, sorry about it's size. As you can see, I have right clicked on the un-allocated area to show the lack of options available.

 

[Jonathan_King]

Hello Darfy,

Try using Partition Wizard to create a new volume in that space. We'll see if a different program can get the job done.

 

[Darfyddi]

Cheers, I will try it in a little later or tomorrow and will let you know how it goes

 

[Darfyddi]

Sorry J_K, I tried both home and demo_pro but both state "This disk uses MBR format, the disk space beyond 2 TB will be unusable." and that is all I can do I wish these programmes allowed copy and paste for their error messages

If there is programme to try that will be great, I am struggling to find anything and am surprised that my mobo doesn't have the software to do it.

 

[cluberti]

You need to use GPT partitions if you want to have partitions larger than 2TB, or a volume that can contain partitions farther out than the 2TB boundary. The MBR partition type has a maximum size of 2TB (which you've created), and on this system it would have been better to create a smaller volume in the RAID utility for the OS and application partition (150-200GB would have worked quite well) with another volume spanning the rest of the space to hold a GPT partition. You cannot mix MBR and GPT partitions on the same volume, hence you cannot use the space above the 2TB limit on that volume - MBR cannot address it, so Windows won't let you do anything with it and thus greys out the menu options in disk management. You need to create 2 volumes in your RAID array - let setup use the smaller one (as an MBR partition type volume), and then use diskmgmt.msc to create a GPT partition type volume on the second (larger) RAID volume. This is the only way you'll be able to use that space, period. It's a BIOS and MBR design/hardware limitation that no software is going to be able to get around, hence there's no software that can do it .

Also note that Windows 7 doesn't create a GPT partition as the boot or OS partition nor can it boot from one either on a BIOS-based PC (hence why setup created that partition as an MBR partition), although an UEFI-based machine could do it (you just have to use diskpart during setup to create the GPT partitions manually, amongst other things).

 

[Darfyddi]

Thank you cluberti, I thought that the 2TB limit was per partition and that I would be able to have the raid volume as:

¦100MB System Reserved¦2047.90GB C: Partition¦746.54GB D: Partition¦

I managed to screw it all up though (before reading your comments) when I tried to partition the unallocated space; I selected the unallocated space and format, the option of the same size came up and I thought 'great' but when it was done, the partition had been done in the middle of the 2049GB partition - 'Oh Bugger' I thought , worse to come though, I couldn't even get it to boot

I am so glad I screwed up in RAID 5 though, none of my spare disks would work (I think my one spare SATA disk is knackered and I can't get my mobo to recognise any IDE disks?) so I ended up taking a disk out the raid, formatting that to put win7 on and then getting the data back from the others, worked a treat - to look at windows folder tree on the raid volume I would never tell a disk was missing . I did use Easeus Partition Master to take the new partition out (not sure if that was necessary) and then I used it to assign a letter to the 2047.90GB partition.

I now have all my documents backed up again, including the ones from the last few days that weren't backed up (although backed up two days before, one was my fiancee's dissertation which had about six hours extra work on it and another was her course work with about four hours work on )

Thank you all for help and advice, I am going to ask about how to set my drives up but will do so in a new thread so not to change the topic of this one.