Raid5 sanity check

[Marc Pelletier]

Hello all,

I have responsibility for a Ibm X360 server with ServeRAID 7k controller.
It has a 6 drive backplane and a 3 drive backplane. We have 4 drives
configured in Raid5, with a single logical drive containing the system and
data partitions. We would like to add more capacity to the system. Our
service provider/dealer tells us that we can't simply add drives and extend
the existing logical drive. He wants to create another raid5 array in the 3
slot channel, which seems rather inefficient.

Almost everything I've read implies that we can do exactly that, but I
can't seem to find anything that explicitly says so to show him. He's the
IBM guy, so I shouldn't really have to, but...

So, can a raid 5 array containing a system partition be expanded by adding
more drives? I want to add the space to the data partition.

thanks

Marc Pelletier

 

[Peter]

How many servers you need to convert that way?

 

[Arno Wagner]

Hello all,

I have responsibility for a Ibm X360 server with ServeRAID 7k controller.
It has a 6 drive backplane and a 3 drive backplane. We have 4 drives
configured in Raid5, with a single logical drive containing the system and
data partitions. We would like to add more capacity to the system. Our
service provider/dealer tells us that we can't simply add drives and extend
the existing logical drive. He wants to create another raid5 array in the 3
slot channel, which seems rather inefficient.

Almost everything I've read implies that we can do exactly that, but I
can't seem to find anything that explicitly says so to show him. He's the
IBM guy, so I shouldn't really have to, but...

So, can a raid 5 array containing a system partition be expanded by adding
more drives? I want to add the space to the data partition.

Assuming you can extend the filesystem, it is theoretically possible
to extend a RAID5 array to more disks, but it would just be a in-place
copy from the old array to the new one with little intermediate storage
(a few secors) needed. I am not sure there are controllers that support
this. You should find out whether yours does. If it is not listed
as a feature, then it cannot do it, since this is not a standard RAID
feature at all.

The way I would do this if the controller cannot do it is to get
enough extra storage (e.g. tape) to completely remove the data and
then move the system to a single (extra) drive. Then you can use the
freed disks and some new ones to create your larger array and restore
the data and system. Since you likely have the above capability
anyways (you have backups, right?), this is a way that should
allways work.

Arno

 

[Curious George]

Hello all,

I have responsibility for a Ibm X360 server with ServeRAID 7k controller.
It has a 6 drive backplane and a 3 drive backplane. We have 4 drives
configured in Raid5, with a single logical drive containing the system and
data partitions. We would like to add more capacity to the system. Our
service provider/dealer tells us that we can't simply add drives and extend
the existing logical drive. He wants to create another raid5 array in the 3
slot channel, which seems rather inefficient.

Almost everything I've read implies that we can do exactly that, but I
can't seem to find anything that explicitly says so to show him. He's the
IBM guy, so I shouldn't really have to, but...

So, can a raid 5 array containing a system partition be expanded by adding
more drives? I want to add the space to the data partition.

thanks

Marc Pelletier

It's called "Logical Drive Migration" & is available for all
ServeRAIDs except the "HostRAID" flavors. Now the 7K is a ROMB & I
believe also an Adaptec "HostRAID." So that's the problem and the
issue to investigate for verification...

 

[Marc Pelletier]

It's called "Logical Drive Migration" & is available for all
ServeRAIDs except the "HostRAID" flavors. Now the 7K is a ROMB & I
believe also an Adaptec "HostRAID." So that's the problem and the
issue to investigate for verification...

Thanks guys, you've been a lot of help. From what I've been able to
determine the 7k is not HostRAID. The 7E is, which is built onto the mobo,
or scsi controller, can't tell which. We have an Ultra320 scsi controller.

cheers

Marc

 

[Curious George]

Thanks guys, you've been a lot of help. From what I've been able to
determine the 7k is not HostRAID. The 7E is, which is built onto the mobo,
or scsi controller, can't tell which. We have an Ultra320 scsi controller.

cheers

Marc

I'm not 100% sure whether it is a hostRAID or not which is why your
continued research is smart. My suspicion that it may be a host raid
comes from the X360 being listed on:

IBM ServeRAID-7e (Adaptec HostRAID)
http://www-307.ibm.com/pc/support/site.wss/document.do?lndocid=MIGR-62492

But on closer inspection the 7K is indeed listed on the regular
IBM ServeRAID 8.25 support CD
http://www-307.ibm.com/pc/support/site.wss/document.do?lndocid=MIGR-61707


So I think you should confront him about Logical Drive Migration
support - and maybe ask IBM for a second (hopefully definitive)
opinion.

Of course there's no reason why you can't follow Arno's advice and
wipe the array, reconfigure a larger one with extra drives and restore
from backup. An imaging utility would of course be recommended (for
the OS at least).

If you NEED 1 array and not 2 he's wrong to shove it down your throat.
Of course there are some advantages to >1 array so you should discuss
with him whether is makes more sense than it first appears - and isn't
just a convenience for him.

Just my $0.02.