Re: Downgrade from RAID6 to RAID5

[DrFranken <midrange@xxxxxxxxxxxx>]

Sounds like a 4-core machine? So an expansion drawer is not an option in 
that case.

We have had good success adding the internal RAID card with the four 
credit card sized 177GB SSDs, it takes 2 slots but you can also add an 
'upper deck' which is four PCIe slots above the power supplies. Me, I 
would mirror those drives as those particular RAID adapters do not have 
write cache.

Once installed you would tag your most popular files with *SSD and you 
get both space and performance.

Advantage:
EASY to install and at no time are you unprotected.
Supported configuration.
Drives and cards readily available at reasonable prices.

Disadvantage:
They are SSD so you need to add to maintenance or self maintain by 
simply buying 1 or 2 extra SSDs. To date we have not seen many of these 
units fail but they are getting older.
You MUST take the machine down to do a maintenance on them since the 
cover comes off.

As to directly addressing the RAID6 to RAID5 migration, others have 
mentioned the full save requirement (not to do the move but to assure 
your data doesn't go away) and the long time required to unstripe and 
restripe.

Performance improvement is there yes as you also remove some reads along 
with the extra writes but won't rock your world.

        - Larry "DrFranken" Bolhuis

www.Frankeni.com
www.iDevCloud.com - Personal Development IBM i timeshare service.
www.iInTheCloud.com - Commercial IBM i Cloud Hosting.

On 11/24/2017 1:53 AM, Don Brown wrote:
> Hi All,
>
> Long story short.
>
> Have a system at 7.3 with 6 x 139GB spinning disks RAID6 and a disk write
> performance issue.
>
> As RAID6 will require three writes to update all striping and RAID5 will
> need two theoretically converting from RAID6 to RAID5 should provide a
> performance increase ?
>
> There is no space for additional drives in this system - Mirrored pair are
> used in Asp02
>
> SSD's is not an option because both IBM and IBM remarketing both do not
> have any of the required drives for this model 8202-E4B
>
> We are considering second hand SSD's but not a preferred option.
>
> Has anyone changed the RAID configuration from 6 to 5 and have any
> comments on the process ?
>
> Thanks
> Don Brown
>
>