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Re: XP Array Storage Layout: Will stripes of LDEV's give me better WRITE throughput than a Single LDEV?

 
Alzhy
Honored Contributor

Re: XP Array Storage Layout: Will stripes of LDEV's give me better WRITE throughput than a Single LDEV?

The LVM example should have read:

lvcreate -L 204800 -i 100 -I 64 /dev/stripeVG


If each LUN is coming from say a 4 way raidset, thin this particular LVOL will essentially engage all 400 Physical Disks.



Or would this be allowed at all in LVM?
Hakuna Matata.
Alzhy
Honored Contributor

Re: XP Array Storage Layout: Will stripes of LDEV's give me better WRITE throughput than a Single LDEV?

Sundar,

My plan is to utilize 8-way stripes - with each member coming from 2 array groups from each ACP controller (on the XP).. Somehow, we've a number of "consultants" that are saying.. we shuould stripe all accross the almost 100 Array Groups that we have - with each array group's LDEVs shared amongst the connected servers...

My initial plan was to allocate a number of array groups per server with that server having exclusive access to the LDEVs of each array group as what I am used to with the Hitachi flavour of the XP...
Hakuna Matata.
Sundar_7
Honored Contributor

Re: XP Array Storage Layout: Will stripes of LDEV's give me better WRITE throughput than a Single LDEV?

LVM would not care. It will stripe the LV across 100 LUNS with stripe size of 64KB.

The size of the LV will possibly be rounded and while creating the VG make sure you set the max PVs to 100.
Learn What to do ,How to do and more importantly When to do ?
Sundar_7
Honored Contributor

Re: XP Array Storage Layout: Will stripes of LDEV's give me better WRITE throughput than a Single LDEV?

As I said, HP recommends to stripe the FS across LUNS from different ArrayGroups. But striping the FS across LUNS from 100 AG doesnt sound good to me.

It would be a good idea to make the LDEVS from different AGs visible to each host rather than having each machine see LDEVs exclusively from certain AGs.
Learn What to do ,How to do and more importantly When to do ?
Jean-Luc Oudart
Honored Contributor

Re: XP Array Storage Layout: Will stripes of LDEV's give me better WRITE throughput than a Single LDEV?

Hi Nelson,

During a benchmark we had our database on XP with no stripping across LUNs and got qlen > 0
We then changed the layout with 2 array groups in our vg swith stripes 8 way, 64K.
Qlen was at zero !
We use RAID 1+0. There is an internal strip in the XP but I don't have the details.
I suppose READ may impact too and unless you have dedicated path for the redo.
Obviously I would recommend RAID1+0 as this would help.
Too me WRITE will go into cache.

Tuning redo will require the help from your DBA. Statspak report will give you hint to where your combined effort (DBA + Sysadmin) should concentrate.

Regards
Jean-Luc
fiat lux
Q4you
Regular Advisor

Re: XP Array Storage Layout: Will stripes of LDEV's give me better WRITE throughput than a Single LDEV?

Nelson,

we have encountered similar ( and very heated debates over this here) issues and found that there is *no rule of thumb*. Agressive stripping may deter the performance. Lot of folks here may haved used "old disks" of a very very high disk latency and their experince may be based on those old tech wrecks. If you buy a truck, it will never be tuned to a racer car.

XP technology has taken care such things internally using extensive caching technology so we don't see such performace hits, right ? The newer hardrive technology and RAID 1+0 are already at work in the back ground. If you stripe too much, every chance that you will kill XP disk performance and HP sales team will be ready at your door step to sell you more cache me & shared memory :)

Large small accesses across 100 disks will bring 100 tracks in the cache and one single byte mod will cause multiple disk access. To complete the commit, all 100 disks have to comply at the same time, weakest disk will drive the performance ( or lack of it) !

Now you decide : Would you consider an 18 wheeler a better performance vehicle since all 18 wheels are rotating or 4 wheeler with more powerful engine making just 4 wheels spin faster ?


IMHO

-Q