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XP512 questions

Roger Baptiste
Honored Contributor

XP512 questions

hi,

I have some questions related to configuring a XP 512 array.

-> What is preferable - RAID 0/1 (mirror/stripe) or RAID 5 . I mean, is the RAID 0/1 performance GOOD on the XP?? That's because i have seen EMC's are mostly configured with RAID 1 , whereas the XP's i have come across were all on RAID 5 and even HP seems to suggest RAID 5.

-> IF i choose RAID 0/1 , will the M1 disks be on L1/R1 and M2 on L2/R2 ? or is there a different method ?

-> Next, how does the concept of EMulation mode works? There seems to be three basic modes,
OPEN-3 -> stripe size of 2.46 gb.
Open-8 -> stripe size of 7.3gb and
open-9 -> stripe of 7.4gb.
So, i would think that if i say i need open-3, all disks in the unit would be striped with 2.46 and the number of splits would be dependent on disk size (like in EMC).
But, it does not seem so in XP. It seems one can use different emulation modes. Will this not affect performance consistency across the RAID?

What is a
OPEN-K/3/8/9/E device?
OPEN-3/K*n OPen-3/K-CVS
LUSE-5
LUSE-7 etc etc.
I was reading the manuals, but couldn't get the full picture on what exactly these names denote. Where does K,E come from?
Is LUSE something like a metavolume of EMC??

-> Is there any choice/flexibility in picking DISKS for an ARRAY GROUP? I mean can we group disks from L1/R1/L2/R2 into an array group?
or would that be an overkill?

-> Any suggestions for stripe size, VG extent sizes etc?

Finally, is there any other utility other than
xpinfo to access XP. (for eg, emc has syminq, symdev, sympd...).

Thanks in advance and points guaranteed for responses! ;-)
-raj
Take it easy.
19 REPLIES
Bernd Reize
Trusted Contributor

Re: XP512 questions

Hi RajMan,

I can at least provide some answers to you:

- Both RAID0/1 and RAID5 are configured in the same physical way: 4 HDDs in the same Disk Frame and the same Disk Bay are called one RAID-Group, which can be 0/1 or 5.
Of course you can mix that, i.e. have 5 Raid-Groups with RAID5 and another five with RAID0/1

- OPEN Emulation
The stripe and split size are independant from the emulation mode, so they should not impact performance.
Which emulation you should choose depends mostly on the disk sizes you need for your hosts and the physical disk sizes within the XP512 - for 15/73/180 GB drives there are recommended OPEN Types to get the most useable space out of the disks.
The different sizes:
OPEN-3 2.461 GB
OPEN-8 7.348 GB
OPEN-9 7.385 GB
OPEN-E 14.568 GB
OPEN-L 36.436 GB
OPEN-M 47.171 GB

OPEN-K i've never heard of.

- CVS/LUSE you are right, they are similar the EMC's Meta Volumes. With CVS you can define smaller volumes (split OPENs), with LUSE you can define larger Volumes (i.e. OPEN-E*1/2/3...)

- You cannot customize the Array Groups, they are hard defined to four disks. But you can build LUSEs that spread over different array groups. But in my opinion you should not use this but host level sriping instead. Much more flexible.

- For stripe size (=stripe depth) HP recommends 64K, VG Extend size i'm not sure.

- There are some cli tools for BCVs and CA, but configuration can be done only via the GUI :-(

Hope that helps,
Bernd

Re: XP512 questions

Hi RajMan

Wow - you ask quite a bit of questions; I will try and answer as many as I can;

You Asked:

What is preferable - RAID 0/1 (mirror/stripe) or RAID 5 . I mean, is the RAID 0/1 performance GOOD on the XP?? That's because i have seen EMC's are mostly configured with RAID 1 , whereas the XP's i have come across were all on RAID 5 and even HP seems to suggest RAID 5.

My response:

I believe the RAID preference should be based on your unique circumstance. That is RAID 0 - stripe; high I/O access but very little amount of redundancy. RAID 1 - mirror but 'slower' I/O access however it provides you with great redundancy; RAID 0/1 combines both High Redundancy/Availability and fast I/O Access.
You can see now that it would depends on you requirements - it you need to write a large volume of data quickly and redundancy is not a concern - then RAID 0. (in short; speed vs security)

For RAID 5 - use at least 1 disk more than RAID 0/1. This aditional disk is for parity - So the first consideration is: You will need more disk for the same job - concern; cost. However, in RAID 5 - data is split and written between two or more disk simultaneously, I/O is increased over the other RAID configuration and also - it provides security and peace of mind since it also has parity written on a seperate drive;
Parity can be used to recover data; so RAID 5 is fast and very safe. So you will have to balance between cost (for the extra disks - for parity)and speed. It depends on your tolerance level.

If cost is not a factor RAID 5 all the way!!!
As far as I know, there aren't any differences because of RAID levels on the XP512 or the EMC. That is, if both Arrays has identical RAIDS, performance will not be better on one or the other because of RAID. performance differences will be because of other factors. XP512 performs much better than EMC under most maybe all circumstances. I must say though that the SVP system software on the EMCs are really cool!

I will end here and answer the other questions in another post.

Hope that help!
The greatest risk one take is not taking one!

Re: XP512 questions

RajMan

ther you go --> Bernd answered some of your questions:

You Asked:

Finally, is there any other utility other than
xpinfo to access XP. (for eg, emc has syminq, symdev, sympd...).

My Response:

Yes there are several other utility/software bundles and plug-ins to access XPs. They are usually included with the package you order; for instance there is a product called AutoPATH XP; which allows you to configure failover I/O path among other stuff. It is included in the SureStore E autoPATH XP software for different platforms; ie. HP UX, AIX, Solaris etc. A utility called datapath "set, query etc") is provide. the only things is I find working with XP software really cool as you move various platforms - you pretty much have the same GUI and commands (with some exceptions)

For more info - check this link out.

http://www.hp.com/products1/storage/disk_arrays/xpstoragesw/index.html

Hope that help!
The greatest risk one take is not taking one!
Roger Baptiste
Honored Contributor

Re: XP512 questions

Bernd,

Thanks for the response. Some more queries;-)

In RAID 0/1 -> Where do the M2 (mirror) disks
sit? Is it predefined (like in
EMC). For example, is
Diskbay on L1 mirrored to a
diskbay on R2 ?

In RAID 5 -> since 4Hdds can only belong to
a raid group, does that mean, max size of a
raid group would be 4*disksize*75% eg:
for disk size of 36Gb -> raidgroup would
be 4*36*3/4 = 108 Gb ?

OPEN Emulation modes ->
is it a term to define a LUN size, as seen by the system?? For eg, if i say i need
OPEN-3, would it mean that i get 3 Gb PV's(lun) at the system end?


thanks
-raj
Take it easy.
Roger Baptiste
Honored Contributor

Re: XP512 questions

Haniff,



Actually, i think it is the reverse. In
Raid 0/1, each HDD has m1 and m2 (mirror disks). So, ever disk needs a mirror.
The usage would then be 50% of the Symm capactiy.

In Raid 5, every group needs a parity disk.
So, for a group of 4 disks, one disk is used
as parity. The usage would then be 75% of the
symm capacity.

With this, if there is enough $$ and capacity, RAID 0/1 is the way to go. But again, it depends on the design of a symm too. EMC seems suited for 0/1. I don't know about XP though.

-raj
Take it easy.
Insu Kim
Honored Contributor

Re: XP512 questions

OPEN Emulation modes ->
is it a term to define a LUN size, as seen by the system?? For eg, if i say i need
OPEN-3, would it mean that i get 3 Gb PV's(lun) at the system end?

> The XP disk array can be designed for several kind of systems such as OPEN systems and Mainframe.
For example,
OPEN emulation (OPEN3,8,9,E, etc) is for OPEN systems and 339X emulation for Mainframe respectively so you need to select an emulation type appropriate for your purpose.
After formatting with OPEN-3, ioscan will display a 3GB device file.

Hope this helps,
Never say "no" first.
Insu Kim
Honored Contributor

Re: XP512 questions

In RAID 5 -> since 4Hdds can only belong to
a raid group, does that mean, max size of a
raid group would be 4*disksize*75% eg:
for disk size of 36Gb -> raidgroup would
be 4*36*3/4 = 108 Gb ?

> For example,
A disk capacity is 47GB and 4 disks are configured with RAID5, OPEN-9 (7.004GB).

47GB * 3 = 141 GB ( Considered RAID5 )
141 GB / 7.004 = 20.131 EA(s),
ioscan will show you 20 LUNs, the total size would be,
20 * 7.004 = 140.08
As a result, you'll lose the remainder, (141-140.08).

This is not the exact caculation so you'll lose much more capacity than you thought it would be.
- I have no data at this time. sorry for this.

For the maximum use of capacity, HP will tell you which emulation you have to choose for a given disk drive like 47GB or 72GB.

Hope this helps,
Never say "no" first.
Victor BERRIDGE
Honored Contributor

Re: XP512 questions

 
Victor BERRIDGE
Honored Contributor

Re: XP512 questions

Forgot:
Load your XP512 with 73GB/10 rpm disks (I think HP P/N A5968AX) they are the best deal...

All the best
Victor
Insu Kim
Honored Contributor

Re: XP512 questions

Hi again,
One of your questions is,
In RAID 0/1 -> Where do the M2 (mirror) disks
sit? Is it predefined (like in
EMC). For example, is
Diskbay on L1 mirrored to a
diskbay on R2 ?

> Disks are sold in groups of four drives called array groups and RAID 1 copy is within the same array group.
For example, the first array group is installed in front bottom, up, over to back and down, then up like the letter N in the bottom of the frame of R1.
This is too difficult to explain everything so I recommend that you refer to the user's manual.

Hope this helps,
Never say "no" first.
Dave Wherry
Esteemed Contributor

Re: XP512 questions

RajMan,
I'll take a swipe at answering some of these. My experience is just on the XP256. I assume it all applies to the 512 also.

Raid 0/1 or Raid 5. Disks are installed in an XP 4 drives at a time. This is called an Array or Marketing group. Over the years we've been told that Raid 5 will give you better read performance, but worse write performance. So, depending on your application, choose your raid level. If it's a read intensive application like Decision Support where people are doing a lot of lookups, use Raid 5. If it's a data acquisition system, stock transactions or gathering statistics, use Raid 0/1. A couple of years ago I got a white paper from Hitachi showing that their Raid 5 performs as well or better than Raid 1. It makes sense. All of your writes go to that massive cache. The disk latency is greatly reduced if not eliminated. Raid 5 performs very well.
So the next part of the Raid question is usable space. Remember you use 4 disks together. In Raid 0/1 you wil have 2 primary and 2 mirror disks. The best you could get is half the space available. With Raid 5 you have 3 data disks and 1 parity. More usable disk space, thus lowering your costs.
That array group that is installed is put in the same cabinet. Beyond that, they are put on the same ACP (bus). They can not be split up. So to answer your L1/L2 M1/M2 question, they are on the same ACP in the same cabinet. You can not split these up.
One other thing, you can not mix Raid levels on an ACP. You can have Raid 0/1 on one of the ACP's and Raid 5 on the other ACP. That was my original configuration. I have since converted everything to Raid 5.

You Open emulations is basically partitioning the drives. If you put an array group of 73GB drives in and format them as Raid 5, Open-8, you will get 29 logical devices (LDEVs), each ~7GB. 4 times 73 is 292GB. 29 times 7GB is ~203GB of usable space. When these drives are formatted, you lose a good deal of space in overhead. Just on a cost basis look for the emulation that gives you the most usable space.
As someone else said LUSE is similar to a metavolume. In Unix I prefer to use just the standard emulations and do host based stripping. For NT, we are using LUSE because those hosts prefer to see a larger device, rather than many small ones. A LUSE device can be up to 32 LDEVs and must be consecutive LDEVS. So they may be on the same array group, span array groups, or be on several array groups. It depends how the LDEVs are numbered/dispersed when the drives are formatted.
A CVS device is a custon volume. Your host needs a command device to talk to the XP. A command device is an LDEV that is only used as a command device. A utility called Volume Size Configuration allows you to slice off a smaller chunk of an LDEV to use as you please. Why waste a 7GB LDEV as a command device when you can make a Custom Volume (CV), say 64MB to use as the command device, leaving the remainder available for other use. Or, you only need a 1GB LDEV for an NT box. Create a smaller CV instead of wasting a whole 7GB LDEV.

...choice or flexibility in picking disks for an ARRAY GROUP?...
Short answer, no. Remember, 4 drives at a time in an array group.

I won't get repitive on the other questions. Others have done a fine jobs answering those.
Roger Baptiste
Honored Contributor

Re: XP512 questions


Thanks for the response. Some of my doubts seems to have cleared. Here is a summary of my intrepretation. Pls clarify , if i am wrong.

**
RAID -> I guess, i will use RAID 5, since the design of XP seems more tuned for RAID 5.
I don't see any point in going for RAID 1, when the disks and disk adaptors are shared by M1 and M2 and that too being housed in the same rack. (unlike in EMC ).

Array group -> pretty much predefined and there is nothing much which can be tinkered. Four disks all from the same rack
make an array group. Nothing more, nothing less?
Number of arraygroups = numberofdisks/4
(approx) ??

Emulation mode -> From the responses, i understand Emulation basically defines the
size of a LUN (which is got from the carving of array groups). I have to decide between
OPEN-9 and OPEN-E (ah! E in hex is 14 and that explains the 14 gb lun ;-) ). The size of lUN in turn defines the number of LUNS!.
Use only one Emulation mode for consistency and ease of maintenance!?

VG configuration -> I plan to pick LUN
from each ACP to create a VG. That way, i spread that VG load across all ACP's , disks, and channels.

VG-LV striping -> Not decided on it. 2 Mb
distributed extents is what i use on EMC (but that is with MEtas). Need to consider lv striping of 64 MB.

and ofcourse EMC <->XP translation is :-)
Disk director <-> ACP
FA director <-> CHIP
META <-> LUSE
VCM <-> CVS

Right?
***

Few more questions ;-)

What is a Control unit?? Is it ACP? or some sort of logical entity? How do we define it?
(or isit predefined? )

Any info on Sharedmemory? (do we need to tune or configure it?)

Is there something corresponding to EMC's "Rule of 17" in XP?? (Rule of 17 is the way the EMC's FrontEnd(fibre/scsi) directors are protected. Each FA is numbered and has a failover FA .

Also, in EMC i can see which FA (frontend director) a LUN is going through by using
symdev command. It helps in tracing the path of the LUN right from the system to the frontend. I don't see xpinfo giving that info. Is it the "PORT " info in the xpinfo output?


thanks again
-raj




Take it easy.
Bernd Reize
Trusted Contributor

Re: XP512 questions

Hi RajMan,

Array group -> exactly right

Emulation -> right, they differ only in their size. You have to make the choice between number of LUNs and size of one LUN. Using the same Emulation for all disks in one box should be the easiest way -- we didn't follow that and mixed OPEN-8 and -E's and got some maintenance problems out of it ;-)

VG config: exactly right. It is the optimal configuration to use a "round-robin" like way

your EMC<->XP translation is right, too


Control Unit: Just a term for internal adressing of LUNs (OPENs). One LUN is adressed by ControlUnit:LUN-Number. I think you could freely choice how to define CUs, but I would recommend using one CU per ACP. This way, the disks have all the same number per ACP, and one VG would i.e. use disks 0:00, 1:00, 2:00 and 3:00, the next VG would get the *:01 disks and so on.

SharedMemory: not configurable afaik. Tuneable is the Cache Layout: how much may be used for WriteCaching (in %). It is called "Duplex Write Cache Limit" I think. Depends of course on your workload, but may be worth tuning.

The XP Port Naming if different from EMC's: All Ports are divided into two halfs, the left and the right one. They are called CL1 and CL2 (Cluster) Within each Cluster there are the CHIP's, named A,B,C.. and so on. For ease of use/maintenance you should use them in pairs: i.e. CL1-A and CL2-A for HostA
You are right, you can see the used port in xpinfo output as 'PORT'

Bernd
Duncan Edmonstone
Honored Contributor

Re: XP512 questions

RajMan,

Remember that you can have a maximum of 256 LUNs per port, so if you have many systems redundantly acessing many disks and maybe many business copies too, you should use a larger emulation mode, or you may find yourself running out of ports.

HTH

Duncan

HTH

Duncan
Roger Baptiste
Honored Contributor

Re: XP512 questions


Bernd, Thanks for your response. I guess, i have some broad idea now on the issues which needs to be addressed for configuring.

Will post back later with any further tuning questions, as i get started into it !

Thanks again everybody.
-raj
Take it easy.
Steve Bonds
Trusted Contributor

Re: XP512 questions

I found a great HP publication which describes in detail the OPEN-(whatever) specification.

http://www.hp.com/cposupport/manual_set/lpg28610.pdf

Found via Google search on "hitachi open-9 cylinders heads sectors". ;-)

To summarize (in case the link goes away):

------
Type sectors cylinders size (MB)
------ ------------ -------- ----------
OPEN-3 4806720 3338 2347
OPEN-9 14423040 10016 7042
OPEN-K 3661920 2543 1788
OPEN-8 14351040 9966 7007
OPEN-E 28452960 19759 13888
OPEN-3*n 4806720*n 3338*n 2347*n
OPEN-9*n 14423040*n 10016*n 7042*n
OPENK*n 3661920*n 2543*n 1788*n
OPEN-8*n 14351040*n 9966*n 7007*n
OPENE*n 28452960*n 19759*n 13888*n
------

ALL of these have 512 bytes per sector, 15 heads, and 96 sectors per track.

(I hope the crude ASCII formatting is readable after I post it...)

-- Steve
Steve Bonds
Trusted Contributor

Re: XP512 questions

Well, the crude ASCII formatting is mangled. Try cutting and pasting into a text viewer that uses a fixed-width font.

-- Steve
Vincent Fleming
Honored Contributor

Re: XP512 questions

WOW - We've got a LOT of XPerts out there! It does my heart good to see everyone so helpful!

One thing to point out... about the shared memory...

Shared memory does take a little configuring... but this should be done by an HP technical consultant (TC - now called SA). The shared memory keeps all the housekeeping info, and needs to be bigger for bigger arrays (basically). You will need to increase SM if you use Continuous Access, Business Copy, want more than 1024 LUNs, and it's recommended for more than 16GB of cache.

Good luck!
No matter where you go, there you are.
Dave Wherry
Esteemed Contributor

Re: XP512 questions

Just an echo on Vincent's comment about getting HP technical help when configuring shared memory. I have an XP256 and we put in the maximum shared memory and cache. Maximum can't be a bad thing can it? Yes it can.
We also had 73GB drives and were doing Business Copy. To do all the Business Copy pairs we needed, we actually had to remove 2GB of cache.
There are several hidden gotcha's when configuring an XP so do work with HP. Also be sure to ask questions about upgrades and how that could affect the configuration in the future.

Dave