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 Post subject: Changing the RAID layout and future upgrades
PostPosted: Thu Aug 30, 2018 1:15 am 

Joined: Tue Nov 19, 2013 4:38 pm
Posts: 119
I need advice going forward on our 3PAR 8400 4 node.
It has 4 cages in total (including the ones with the controller nodes).
We initially bought it with 48 3.84TB SSD drives and are running RAID5 7+1 (magazine availability). We subsequently expanded the system by 8 disks now total of 56 Disks and remained on RAID5 7+1.
This is now an unbalanced system.

We are going to expand the system again with another 8 disks and we will have 64 disks in total. This makes me consider my options.

I prefer to change the RAID layout to RAID6 for better resiliency (even though we never had any disk failures). I could go for RAID 6 14+2 without loosing any usable space compared to the current RAID level.

Would this be a good idea?

However, if and when we need to expand again the next balanced configuration is with 96 disks which is too big a jump for the money men :roll:

How big a deal is it to run the system unbalanced anyway?

What would you guys do?

Thank you :D


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 Post subject: Re: Changing the RAID layout and future upgrades
PostPosted: Thu Aug 30, 2018 2:23 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1570
Location: Europe
skumflum wrote:
I need advice going forward on our 3PAR 8400 4 node.
It has 4 cages in total (including the ones with the controller nodes).
We initially bought it with 48 3.84TB SSD drives and are running RAID5 7+1 (magazine availability). We subsequently expanded the system by 8 disks now total of 56 Disks and remained on RAID5 7+1.
This is now an unbalanced system.

We are going to expand the system again with another 8 disks and we will have 64 disks in total. This makes me consider my options.

I prefer to change the RAID layout to RAID6 for better resiliency (even though we never had any disk failures). I could go for RAID 6 14+2 without loosing any usable space compared to the current RAID level.

Would this be a good idea?

However, if and when we need to expand again the next balanced configuration is with 96 disks which is too big a jump for the money men :roll:

How big a deal is it to run the system unbalanced anyway?

What would you guys do?

Thank you :D


I would say go for RAID6. You’re not really unbalanced from a hardware point of view with 56 drives, all cages have 14 drives. The number of drives per node doesn’t add up to the set size, but that is a very small problem.

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 Post subject: Re: Changing the RAID layout and future upgrades
PostPosted: Fri Aug 31, 2018 3:50 am 

Joined: Tue Nov 19, 2013 4:38 pm
Posts: 119
MammaGutt wrote:
skumflum wrote:
I need advice going forward on our 3PAR 8400 4 node.
It has 4 cages in total (including the ones with the controller nodes).
We initially bought it with 48 3.84TB SSD drives and are running RAID5 7+1 (magazine availability). We subsequently expanded the system by 8 disks now total of 56 Disks and remained on RAID5 7+1.
This is now an unbalanced system.

We are going to expand the system again with another 8 disks and we will have 64 disks in total. This makes me consider my options.

I prefer to change the RAID layout to RAID6 for better resiliency (even though we never had any disk failures). I could go for RAID 6 14+2 without loosing any usable space compared to the current RAID level.

Would this be a good idea?

However, if and when we need to expand again the next balanced configuration is with 96 disks which is too big a jump for the money men :roll:

How big a deal is it to run the system unbalanced anyway?

What would you guys do?

Thank you :D


I would say go for RAID6. You’re not really unbalanced from a hardware point of view with 56 drives, all cages have 14 drives. The number of drives per node doesn’t add up to the set size, but that is a very small problem.


Ok, but next time i expand with 8 disk it will get unbalanced from a per node point of view. This is not a problem?


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 Post subject: Re: Changing the RAID layout and future upgrades
PostPosted: Fri Aug 31, 2018 12:01 pm 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1570
Location: Europe
Why? You add two drives to each of your 4 cages.

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 Post subject: Re: Changing the RAID layout and future upgrades
PostPosted: Mon Sep 03, 2018 2:42 am 

Joined: Tue Nov 19, 2013 4:38 pm
Posts: 119
MammaGutt wrote:
Why? You add two drives to each of your 4 cages.


Yes all cages will get equal share of disk but if I run RAID 6 14+2 there will be a unbalance with regards to node ownership of disk and RAID distribution.

I will have 64 when I expand the disk now. This will allow a balanced RAID 6 14+2. The next number of disk is 80 if i insist on a keeping it balanced.... but If I only buys 8 more it will be unbalanced. But is this a big deal?


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 Post subject: Re: Changing the RAID layout and future upgrades
PostPosted: Mon Sep 03, 2018 7:28 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 1570
Location: Europe
skumflum wrote:
MammaGutt wrote:
Why? You add two drives to each of your 4 cages.


Yes all cages will get equal share of disk but if I run RAID 6 14+2 there will be a unbalance with regards to node ownership of disk and RAID distribution.

I will have 64 when I expand the disk now. This will allow a balanced RAID 6 14+2. The next number of disk is 80 if i insist on a keeping it balanced.... but If I only buys 8 more it will be unbalanced. But is this a big deal?

Remember that 3PAR looks at chunklets and not physical disks when growing. You have a balanced system from a hardware perspective (identical config behind each node, identical per backend port DP1/DP2 and identical per cage). You don't have a config per node to match your set size, but with a set size of 16 and 4 nodes you would need a multiple of 64 to stay perfectly alligned there. With SSDs that just isn't reasonable and not really a big issue anymore as it is unlikely that you are going to max the SSDs. If you were even close to that you would have a bigger issue with 8400 and not 8450 vs not writing full sets.

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 Post subject: Re: Changing the RAID layout and future upgrades
PostPosted: Mon Sep 03, 2018 7:46 am 

Joined: Tue Nov 19, 2013 4:38 pm
Posts: 119
MammaGutt wrote:
skumflum wrote:
MammaGutt wrote:
Why? You add two drives to each of your 4 cages.


Yes all cages will get equal share of disk but if I run RAID 6 14+2 there will be a unbalance with regards to node ownership of disk and RAID distribution.

I will have 64 when I expand the disk now. This will allow a balanced RAID 6 14+2. The next number of disk is 80 if i insist on a keeping it balanced.... but If I only buys 8 more it will be unbalanced. But is this a big deal?

Remember that 3PAR looks at chunklets and not physical disks when growing. You have a balanced system from a hardware perspective (identical config behind each node, identical per backend port DP1/DP2 and identical per cage). You don't have a config per node to match your set size, but with a set size of 16 and 4 nodes you would need a multiple of 64 to stay perfectly alligned there. With SSDs that just isn't reasonable and not really a big issue anymore as it is unlikely that you are going to max the SSDs. If you were even close to that you would have a bigger issue with 8400 and not 8450 vs not writing full sets.


Thank you. I will stop worrying about it :D


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 Post subject: Re: Changing the RAID layout and future upgrades
PostPosted: Thu Sep 06, 2018 9:23 am 

Joined: Fri Jul 13, 2018 9:42 am
Posts: 3
Location: Netherlands
Good afternoon,

If you are in need of some 3.84TB SSD's for your upgrade and increase in storage, I have about 70 pcs available, refurbished by HP, like new. I also have 1.8TB, K0F37A drives.
Pls PM me, if you need any specific 3PAR disks or other components.

Regards
Iveta


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