sureshctr
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Symmetrix Disks requires Diskpar

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Why only symmetrix disks requires diskpar or diskpart when it is assigned to a windows host.
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xe2sdc
4 Germanium

Re: Symmetrix Disks requires Diskpar

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Symms/DMX do emulate "virtual" disks that are presented to the host. Behind those "virtual" disks you have a complex mix of real drives, cache (subdivided in tracks), processors and eventually processes that do replicate your data inside the same storages or even on different storages.

You don't really NEED diskpar or other tools to use symm disks.. In fact the disks will work even if not "tuned" with diskpar. You'll always be able to write to the disks and read back your data. You simply loose valuable performances due to mis-alignment between how the host works and how the storage works.

Diskpar is usefull since allows you to allign the way the host does its IO/s to the way the storage handles IO/s. This will give you the best possible performances. That's it.

You have almost the same issues with Clariion .. The difference betweek Clariion and DMX is that Clariion offers you to "align" the partitions from inside the storage. But this is only one of the differences between Clariion and DMX. There are huge differences since they address different needs in a different way. In a word. They are different. :D

I don't really know how other storages work .. Maybe someone else can share its experience with other vendors.

If you try googling a little, you'll find that diskpar is a tool offered by Microsoft (not from EMC) and that it's suggested not only by EMC ;-)

Have fun .. :D
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xe2sdc
4 Germanium

Re: Symmetrix Disks requires Diskpar

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Symms/DMX do emulate "virtual" disks that are presented to the host. Behind those "virtual" disks you have a complex mix of real drives, cache (subdivided in tracks), processors and eventually processes that do replicate your data inside the same storages or even on different storages.

You don't really NEED diskpar or other tools to use symm disks.. In fact the disks will work even if not "tuned" with diskpar. You'll always be able to write to the disks and read back your data. You simply loose valuable performances due to mis-alignment between how the host works and how the storage works.

Diskpar is usefull since allows you to allign the way the host does its IO/s to the way the storage handles IO/s. This will give you the best possible performances. That's it.

You have almost the same issues with Clariion .. The difference betweek Clariion and DMX is that Clariion offers you to "align" the partitions from inside the storage. But this is only one of the differences between Clariion and DMX. There are huge differences since they address different needs in a different way. In a word. They are different. :D

I don't really know how other storages work .. Maybe someone else can share its experience with other vendors.

If you try googling a little, you'll find that diskpar is a tool offered by Microsoft (not from EMC) and that it's suggested not only by EMC ;-)

Have fun .. :D
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xe2sdc
4 Germanium

Re: Symmetrix Disks requires Diskpar

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ThX for your quick evaluation of my reply ..

But think about waiting a little more in the future, just to allow other valuable guys to add their valuable contribution to your interesting thread :D ..

I'm neither an oracle (please note the lower case "o" ;-) nor God .. so maybe I'm wrong to some degree. :D .. And maybe someone may give better/different explanations and share experiences .. :-)
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RRR
5 Tungsten

Re: Symmetrix Disks requires Diskpar

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Like the Italian guy said: you don't need to align a disk, but if you value performance, you would like to do it ! It works with all disks, even the one in your notebook or personal computer at home. AFAIK it's only an issue with IBM compatibles (Windows, Linux, VMware, SUN Solaris (Intel) and it has to do with the MBR (master boot record) taking up 63 sectors in the beginning of each disk, while a track is 32kB or 64kB.
Imagine writing 4kB blocks on a 64kB track with a 63 sector MBR: of the first track 31,5kB is already filled up (MBR) and the remaing 32,5kB is where the first partition is located. The first 8 blocks land on the first track, leaving 0,5kB in the first track. the next 4kB block that will be written will write 0,5kB on this first track, then there's a head movement and the remaing 3,5kB will be written on the next track, so invoking an extra I/O (head movement). If you align the disk, you actually add an extra few unwritable sectors right after the MBR. A value of 128 sectors will make the first 128 sectors unavailable (that's including the MBR). the partition will start not at the 64th sector, but at the 129th sector. The first partition will now start at a "fresh" track and will thus be aligned. I've seen performance improvements of more than 20% !!!



And indeed: don't be so quick in rewarding the Italian guy with points..... Maybe other answers are more valuable ;)
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AranH1
4 Germanium

Re: Symmetrix Disks requires Diskpar

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Stefano,
To add to your comment, even though on a CLARiiON you can specify the alignment when binding a LUN, the recommendation is still to use host based disk management utilities to align the disk. One reason being if you clone or migrate the LUN the alignment is not carried when set using the array tools to create the alignment. The host based alignment of the disk will transfer on a clone or LUN migration since it is the host that created the partition alignment.
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RRR
5 Tungsten

Re: Symmetrix Disks requires Diskpar

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Any thought on why you can do Clariion based alignment ? I know host based is preferred, but if you'd never use the array based aligment, then why is it even there in the first place ?
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RRR
5 Tungsten

Re: Symmetrix Disks requires Diskpar

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Having said that, I realize, this would make alignment of a non replicated LUN which is used for a server's c: drive muuuuuuuuuuuuucheasier. Ever tried to align the c: drive of a windows server ?
- create a LUN
- mask it to another windows server as an extra LUN
- align the drive
- unmask it and mask it to the server it's supposed to be attached to
- start your installation and don't remove the partition tthat you'll find there

This can be a nightmare when you're using RDP to roll out servers, since you'll have to adjust the RDP scripts as well to not delete any partitions and start using what is already found on the LUN
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AranH1
4 Germanium

Re: Symmetrix Disks requires Diskpar

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Yep, that's about the only scenario I can think of where the array based LUN alignment would be preferred. Sounds like you have had lot's of fun with those rollouts ;-)
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RRR
5 Tungsten

Re: Symmetrix Disks requires Diskpar

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Thank goodness it's weekend ! Yeah.

No, actually I've been trying to figure out this alignment of a server's c: drive only once... and it took 2 days to not get it right. And yes, that was with an RDP server, so I indeed did it, done that, ... what's the text again ? Oh well... I'm not an OS guy. I'm glad I'm not. We decided that we don't align the c: drive. Too few IOs anyway. that's even easier. Every other LUN: alignment ! Definately.
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