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Free space on AutoRAID for RAID 0/1

TVS MURTY
Advisor

Free space on AutoRAID for RAID 0/1

Hello,
We have 12H AutoRAID with 8 x 36GB HDD.Till recently, we configured 8LUNS each of about 24GB capacity,with a hot standby. The free space
available was 0.

Now after going through the manuals,we wanted to reconfig. the LUNS, so as to increase the free space available,which can be used for providing RAID 0/1 storage which would give us better performance.So we removed all the LUNS and
recreated by creating 8 LUNS each of 14 GB. So now we got a lot of unallocated free space.

The previous disk config was(after 8 LUNs were created)
--- Disk space usage --------------------
Total physical = 277863 MB *
Allocated to LUNs = 193392 MB *
Used as Active Hot spare = 34732 MB *
Used by non-included disks = 0 MB *
Used for Redundancy = 49739 MB *
Unallocated (avail for LUNs) = 0 MB *
-----------------------------------------

and the earlier output of arraydsp -v
was:
Raid 0/1 blocks = 23977984
Raid 0/1 block length = 512
Raid 0/1 capacity = 11708 MB *

After the recreation of 8 x 14GB new LUNS,the disk config is

--- Disk space usage --------------------
Total physical = 277863 MB *
Allocated to LUNs = 114688 MB *
Used as Active Hot spare = 34732 MB *
Used by non-included disks = 0 MB *
Used for Redundancy = 49739 MB *
Unallocated (avail for LUNs) = 78704 MB *

Now the output of arraydsp -v is,

Raid 0/1 blocks = 11008
Raid 0/1 block length = 512
Raid 0/1 capacity = 5 MB *

I thought the output would show an increase in the RAID 0/1 capacity as we made available more free space or is my understanding of the arraydsp output wrong ?
What should we do to see that we always have RAID 0/1 ? we can efford to have small size LUNS and we need all the 8 LUNS.

Thank you for your time.

Regards,

TVS
6 REPLIES
Vincent Farrugia
Honored Contributor

Re: Free space on AutoRAID for RAID 0/1

Hello,

did you restore data after doing the LUN reconfiguration on the AutoRAID?
Tape Drives RULE!!!
Ian Dennison_1
Honored Contributor

Re: Free space on AutoRAID for RAID 0/1

The first link is a basic one that you probably have already seen.

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x0fd99200caded5118ff40090279cd0f9,00.html

The second link details how to use the ???arraydsp??? command to verify the performance. Check out the ???working set??? value, and if it has an asterisk next to it, you have a problem. I experienced something similar, and found it was the fact I had not entirely removed the previous LUNs and given the AutoRaid time to reconfigure itself.

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0xd4dc9200caded5118ff40090279cd0f9,00.html

Share and Enjoy! Ian
Building a dumber user
Insu Kim
Honored Contributor

Re: Free space on AutoRAID for RAID 0/1

 
Never say "no" first.
TVS MURTY
Advisor

Re: Free space on AutoRAID for RAID 0/1

Vincent/Ian/Kim,

Sorry for not responding. Was away from office and later had trouble accessing forums.

After creating the LUNs and the VG,and later the data I started seeing the RAID0/1 capacity increasing. The linka provided were useful. But I don't see the RAID 0/1 capacity coming down at any point of time.

Does this go on increasing till it hits the limit imposed by the free space available and then start moving data to RAID5? Please clatify.

Thank you for your help.

TVS
Insu Kim
Honored Contributor

Re: Free space on AutoRAID for RAID 0/1

>Does this go on increasing till it hits the limit imposed by the free space available and then start moving data to RAID5? Please clatify.

I think that write working set provided before will give you an answer.
Please read relation between write working set and RAID 1/0 again.

In the previous posting,
if a point is reached where the write working set exceeds the size of the available RAID 0/1 space, some writes will have to be serviced from RAID 5.

Hope this helps,
Never say "no" first.
Insu Kim
Honored Contributor

Re: Free space on AutoRAID for RAID 0/1

To help your understanding, it's important to understand write working set.
Write working set is the number of data blocks written to the disk array over a peirod of time.
The array continually keeps eyes open for the number of write I/Os and updates the write working set to reflect recent write activity.

Once it's defined, the array first services all writes from RAID 1/0 and then compares the amount of RAID 1/0 space available to the write working set.
The amount of RAID 1/0 space available will be reduced over a period of time whereas data space for RAID 5 increases.
Finally,
If a point is reached where the Write Working Set exceeds the size of the available RAID 0/1 space, the disk array will begin servicing writes from RAID 5.

Hope this helps,
Never say "no" first.