Re: Adding hot spare using a disk from an existing RAID 5 string

Exactly right. The 051 is a hot spare.


- Larry "DrFranken" Bolhuis

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

On 6/5/2017 4:31 AM, Marco Facchinetti wrote:

Thanks for your suggestions. Sadly the customer said the risk was
acceptable and took from 08:20 to 23:48 to complete!.

What I saw (and looks a little strange to me) is that the disks before the
modification were declared model 099 and 090 (same type 19A1). Once I
modified the raid adding the hot spare al the raided disk became model 099
and the hot spare 051. Is that right?

TIA

--
Marco Facchinetti

Mr S.r.l.

Tel. 035 962885
Cel. 393 9620498

Skype: facchinettimarco

2017-06-02 18:06 GMT+02:00 Marco Facchinetti <marco.facchinetti@xxxxxxxxx

:

Helps a lot, thanks. I'll ask the customer if he is willing to take the

risk.

Best regards

--
Marco Facchinetti

Mr S.r.l.

Tel. 035 962885
Cel. 393 9620498

Skype: facchinettimarco

2017-06-02 15:04 GMT+02:00 DrFranken <midrange@xxxxxxxxxxxx>:

It's not really a Power7 thing it's as SAS vs SCSI thing. But since

Power7 is 100% SAS it will be true on Power7. Power5 was all SCSI and
Power6 was the stepping stone where you could mix SAS and SCSI disks
with i
7.1.

So the issue is that on SCSI disks when we RAIDed a set of disk the RAID
card looked at the number of drives you had selected for that set and
wrote
the RAID stripes onto only some disks. For 3 drives it used 2. For 4-7
it
used 4 and for 8-11 it was 8 and I believe it used 12 for 12-18 drives
which was the largest RAID sets of the day. The other disks were
protected
but didn't contain RAID stripe data so theses disks could be removed
from
the set without breaking it. Internal to the RAID card it will simply be
declared to contain all zeros. With that the RAID calculations worked.
You
can also ADD to the RAID sets and those new drives are protected also
but
with no Stripe. The raid card assumes they contain all zeroes,
initializes
the drive to contain all zeros, and protection begins from there.

With SAS however the game changed. No matter how many drives you have
when you start RAID they all get a percentage of the RAID data. 8 9 10
disks, whatever, it's evenly split. This is better for performance all
around. However that means in a Power7 CEC with it's 8 drives you're
going
to have all 8 with strip. (Curiously with SCSI you would have also since
it's 8 :-) ) Back in the Power5 days we saw a lot of companies putting
in
lesser numbers of drives to start but with the price of drives dropping
so
fast, most Power7 systems shipped with the full compliment of 8. I
cannot
recall a single customer who did not install 8 drives to start.

I mentioned that you MIGHT find that a drive could be removed and that
would occur if you had started with say 6 drives and then added two
more to
the set at a later time. This is still allowed with SAS as it was with
SCSI
but it is NOT recommended. If this had been done then 6 drives in the
set
will appear smaller than the other two. Those two would be candidates
for
step 6 in this case. So possible but unlikely.

Hope that helps!


- Larry "DrFranken" Bolhuis

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

On 6/2/2017 7:08 AM, Marco Facchinetti wrote:

Thanks Doc, do you mind explaine why on a power7 step 6 will drive to

step
7? I'm not a specialist so this is not obvious to me.

TIA

--
Marco Facchinetti

Mr S.r.l.

Tel. 035 962885
Cel. 393 9620498

Skype: facchinettimarco

2017-06-01 20:49 GMT+02:00 DrFranken <midrange@xxxxxxxxxxxx>:

Error! Note the added ** NOT ** in the first line below.

On 6/1/2017 2:32 PM, DrFranken wrote:

You will with near certainty be ** NOT ** able to use option 6 on a

Power7

machine. Yes there is a scenario I can imagine where it could happen
but
not likely.

That means you will be using option 7 (Stop RAID) and THAT means you
WILL have a full backup of your system before you attempt this
procedure. It is NOT an option.

Rob is right that you could use ASP balancing to drain the drive but
why
not go into SST and simply remove the drive. This will completely
drain
it AND remove it from the ASP. This can run while the system is still
up.

After that you can do your backup, boot to SSD, End RAID, then start
that drive as a hot spare and then start RAID again.

- Larry "DrFranken" Bolhuis

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

On 6/1/2017 2:23 PM, Rob Berendt wrote:

Verify from others.

That being said I wonder if you could minimize your downtime by
removing
data from the disk, or at least as much as you can, beforehand.
See:
STRASPBAL TYPE(*ENDALC)
STRASPBAL TYPE(*MOVDTA)


Rob Berendt

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