VRAID

 
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ilayy
Regular Advisor

VRAID

hi expert i am soo confused of the calculation of VRAID 5 and VRAID 1 and also the protection level.
1) first i have read on a forum that the protection level is needed only when i am using VRAID1 but it is not usefull when i am using VRAID 5 is that true ? and why?

2)on another forum i read that The EVA *always* binds two disk drives together as a 'pair' which it uses to store VRAID-1 data, even when you don't use any virtual disks with VRAID-1.so which means that even if i am using RAID5 eva will keep the half of my capacity and in this case what does it mean to have a protection level?

3) how to calculate the capacity when using RAID 1 for example i have 01 diskgroup with 7x146GB+4x36GB 'protection level' of 1 and leaving about 10 raw

please expert help me to understand

7 REPLIES 7
susanta_dutta
Trusted Contributor
Solution

Re: VRAID

Hi ilayy,

Protection level is not related to any Raid Levels - vRaid1 or vRaid5. Protection level is just to reserve some space in the disk group - This reserved space would be used in case of any drive failure. If you leave some sufficient space unused in a disk group, you may not need to enable Protection Level. That unused space would be used, in case of any disk Failure, when you replace the failed drive with a new one.

In vRaid1 data mirrored between one pair of drives, so you loose 500% of your space, whereas for vRaid5 data is distributed with small piece of chunk across all the drives with Data & parity ratio of 4:1, so you loose 20% of your space.

Hence both of your first statements are incorrect.

For an example, if you have 10 disks of 10GB in a disk group and configured single protection level, you would have 10 X 10 â 10 X 2 = 80GB space. For single protection two drive space would be reserved, this is done to support impact of maximum raid level that is vRaid1. Now you can create a Vdisk of vRaid1 max 40GB(80 X 0.5) or a vRaid5 of max 64GB(80 X 0.8 ). Lets say, you created a Vdisk of 10GB, so you used 20GB. Now you are left with 60GB. . Now again you can create a Vdisk of vRaid1 max 30GB(60 X 0.5) or a vRaid5 of max 48GB(60 X 0.8 ). And so on.

To answer your specific question, 7x146GB+4x36GB 'protection level' of 1 and leaving about 10 raw, Each drive you need to multiply by 0.93 to get the actual formatted capacity. So 146GB would be somewhere around 136GB. Single protection level would result into reserving 136 X 2. Your raw capacity would be around 812GB. If you want to leave 10GB raw space, you would be able create a Vdiak of vRaid1 approximately 400GB size or vRaid5 Vdisk of 640GB


For performance perspective, Its not good to mix different drive size within same disk group, because bigger disk would have more data and controller access it more than the small diskâ ¦Hence there would be imbalance within the drives.

Regards
Susanta
susanta_dutta
Trusted Contributor

Re: VRAID

Forgot to complete one sentence:

That unused space would be used, in case of any disk Failure, when you replace the failed drive with a new one, you get the unused space back
ilayy
Regular Advisor

Re: VRAID

hi again
first thanks for your reply
as i understood that the spare space is used to reconstract the failed disk.my question is if i have no spare space reserved even i don't have enough unlocated space to reconstract the failed disk the data will be lost or when i replace the disk the reconstraction will occur? for example
i have only 9 disks (146 GB) and 1 disk 72 GB in my enclosure the first 8 disks(146 GB) form 1 disk group and the last 2 disks (146+72) are not allocated .in my disk group just i have 1 VDISK (RAID 1) which occupy all the space (584 GB) and i have no protection level so if one disk fails i will loose the data or when i replace the failed disk data will be rebuilt?
i am triing to understand
Marcus Schack
Trusted Contributor

Re: VRAID

Normally you would not want to mix disks in a disk group if different sizes and speeds. So here is what I would recommend. Put all your 146GB disks into one disk group and leave the one 72GB out. Give the 146GB disk group a sparing level of 1. Then create the Vraid5 and Vraid 1 LUNs that you need. In general, a Vraid5 LUN has about a 28% overhead. You will see how much room you have available when you create the LUNs in Command View
ilayy
Regular Advisor

Re: VRAID

hi all
what i am triing to do is to understand the protection level for this i gave the example of mixed drives capacity in same disk group.i meant that the protection level is used to rebuild data what ever if i am using VRAID 1 or 5. so i am asking if i set the protection level to 0 and i have no sufficient unassigned space in the disk group and if a disk fails what happen data is lost or when i replace the disk data is rebilt again? i will formulate again my example.
if i have set the protcetion level on the disk group to 0
the disk group is formed of 8 disks (146 gb) and i create a VDISK of (1168 gb) so i assigned all the space and i am using RAID 5 or 1 it is the same if a disk fails what happen? if i replace the disk data will be rebuilt on the new disk or data is lost as i don't have spare space neither anunssigned space in the disk group? just i am triing the protection level
Víctor Cespón
Honored Contributor

Re: VRAID

Let me try to symplify it for you:

Aa disk fails, the controllers see that and the most prioritary task is rebuilding the RAIDs then.

If there's enough free space on the disk group it will use that.

If not it will see if there's space reserved (disk failure protection)

If there's no free space anywhere, it waits until you replace the disk.

You do not lose data because of single disk failure (only if it's on VRAID 0).

The rebuild operation is given priority over all other tasks, so the system is back to fully redundant as soon as possible.

Once the rebuild is finished, another disk failure will lead to this process being repeated.
ilayy
Regular Advisor

Re: VRAID

thanks alot now it is clear for me