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2 Intern
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294 Posts
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66138
September 22nd, 2011 07:00
Volume Over-Subscribed Question
Hi,
I was wondering why my volume is "over-subscribed" when I have enough space on the pool? Here are some background information of my configuration:
PS6000E - 7.2k SATA drives - 8 TB base - 16 x 500 GB - RAID 50 - 5.23 TB after RAID 50 - Name: R50
PS6000XV - 15k SAS drives - 9.6 TB base - 16 x 600 GB - RAID 10 - 3.66 TB after RAID 10 - Name: R10
On the R10 array, I have 1.43 TB of free space and on the R50 array, I have 2.1 TB of free space.
On the Pool Capacity pie chart, it says 4.85 TB (54.6%) for Volumes, 3.46 TB (38.9%) for Snapshots, 587.9 GB (6.5%) for Free Space.
All of the volumes are Thin Provisioned.
So on one 400 GB volume, In-Use volume space is 136.26 GB, Free 63.33 GB, and Unreserved 200 GB. Snapshots In-Use is 6.99 GB and Free 93.02 GB.
Distribution of Volume Across Members: R10: 313.83 GB; R50: 85.8 GB
Volume Distribution Info says: RAID Preference: RAID 50; Status: over-subscribed; Load Balancing: Enabled.
Does anyone know why it's considered to be over-subscribed and how to fix this? Why is the R10 basically taking over this volume when it has a RAID preference of RAID 50? Also, can someone please direct me to some literature or links so I can educate myself about this?
Thank you in advanced!
dajonx
2 Intern
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294 Posts
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September 22nd, 2011 12:00
Joe,
Thank you for your response.
After playing around for a while, I was able to get the Distribution of Volume Across Members back to the R50 array after I:
1) Decreased the number of total snapshots saved -- From four to three snapshots
2) Deleted all of the existing snapshots and created a new snapshot backup
3) Decreased the Snapshot Reserve percentage
After doing all of those things, the storage pool pie chart says: Reserved for Volumes 4.85 TB (54.6%); Reserved for Snapshots 1.58 TB (17.7%); Free Space 2.46 TB (27.6%).
The free space on each array is now: R10 2.04 TB; R50 2.12 TB.
So now, it's been resolved.
Is it safe to say that in this case, the volume was "over-subscribed" due to the snapshots using too much space?
Joe S586
9 Technologist
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729 Posts
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September 22nd, 2011 11:00
dajonx,
Based on your description, it seems that the volume is not properly honoring the RAID preference. We will need you to open a support case so that we can look at both arrays to see what is going on. Prior to opening the case, please run the diags from both members.
Regarding additional information about load balancing, go to: support.equallogic.com/.../tech_reports.aspx (support user account login required) and you should see the document titled: Using Tiered Storage in a PS Series SAN.
Regards,
Joe
Joe S586
9 Technologist
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729 Posts
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September 22nd, 2011 13:00
dajonx,
The behavior you described would be normal and what would be expected. Snapshots share the same volume pages as the base volume, so they would live on the same member as the base volume. By deleting snapshots, you freed up enough space for the base volume pages to move to the correct member for your RAID preference.
So, you don’t need to open a support case.
Regards,
Joe