[gpfsug-discuss] Rebalancing with mmrestripefs -P

Luis Bolinches luis.bolinches at fi.ibm.com
Tue Aug 21 05:11:24 BST 2018


Hi

You can enable QoS first to see the activity while on inf value to see the
current values of usage and set the li is later on. Those limits are
modificable online so even in case you have (not your case it seems) less
activity times those can be increased for replication then and Lowe again
on peak times.

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> On 21 Aug 2018, at 1.21, david_johnson at brown.edu wrote:
>
> Yes the arrays are in different buildings. We want to spread the activity
over more servers if possible but recognize the extra load that rebalancing
would entail. The system is busy all the time.
>
> I have considered using QOS when we run policy migrations but haven’t yet
because I don’t know what value to allow for throttling IOPS.  We need to
do weekly migrations off of 15k rpm pool onto 7.2k rpm pool, and previously
I’ve just let it run at native speed. I’d like to know what other folks
have used for QOS settings.
>
> I think we may leave things alone for now regarding the original
question, rebalancing this pool.
>
>  -- ddj
> Dave Johnson
>
>> On Aug 20, 2018, at 6:08 PM, valdis.kletnieks at vt.edu wrote:
>>
>> On Mon, 20 Aug 2018 14:02:05 -0400, "Frederick Stock" said:
>>
>>> Note you have two additional NSDs in the 33 failure group than you do
in
>>> the 23 failure group.  You may want to change one of those NSDs in
failure
>>> group 33 to be in failure group 23 so you have equal storage space in
both
>>> failure groups.
>>
>> Keep in mind that the failure groups should be built up based on single
points of failure.
>> In other words, a failure group should consist of disks that will all
stay up or all go down on
>> the same failure (controller, network, whatever).
>>
>> Looking at the fact that you have 6 disks named 'dNN_george_33' and  8
named 'dNN_cit_33',
>> it sounds very likely that they are in two different storage arrays, and
you should make your
>> failure groups so they don't span a storage array. In other words,
taking a 'cit' disk
>> and moving it into a 'george' failure group will Do The Wrong Thing,
because if you do
>> data replication, one copy can go onto a 'george' disk, and the other
onto a 'cit' disk
>> that's in the same array as the 'george' disk.  If 'george' fails, you
lose access to both
>> replicas.
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>>
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