Shadowset can have different sizes of disks ?

[kiran kumar kolluru]

Hi,

Sorry If I am asking very basic question.

1. Can a shadow set have different sizes of
disks. ( I feel all the members of a
shadow set should be of same size)
2. I created a shadow set with 3 DGA divices
as members. I am viewing the size of
shadowset is same as primary member od
shadowset.
3. Is there any possible way in Alpha-VMS
to combine different sizes of disks in
to one logical disk. When I see the size
of the logical disk, it has to show me
the total size of all the disks in that
logical set.

-thanks in advance
Kiran

[Martin Vorlaender]

Kiran,

>>>
Sorry If I am asking very basic question.
<<<

No need to apaologize - we're here to help.

>>>
1. Can a shadow set have different sizes of
disks. ( I feel all the members of a
shadow set should be of same size)
<<<

This is the last restriction that fell with the advent of VMS 7.3-2.

>>>
2. I created a shadow set with 3 DGA divices
as members. I am viewing the size of
shadowset is same as primary member od
shadowset.
<<<

Nope. The DGA device will have the size of the smallest member.

>>>
3. Is there any possible way in Alpha-VMS
to combine different sizes of disks in
to one logical disk. When I see the size
of the logical disk, it has to show me
the total size of all the disks in that
logical set.
<<<

What you're looking for is called a volume set under OpenVMS. See e.g. http://h71000.www7.hp.com/doc/732FINAL/aa-pv5mh-tk/00/00/88-con.html

HTH,
Martin

[Mobeen_1]

Kiran,
Please find below answers to your queries.


Can a shadow set have different sizes of
disks. ( I feel all the members of a
shadow set should be of same size)

The answer to the above question is YES & NO
YES - You could have a 9GB disk that is the
master and you could have 2 18GB shadow
set members
NO - You cannot do the reverse of the above,
you cannot shadowcopy 18GB disk to 9GBs


I created a shadow set with 3 DGA divices
as members. I am viewing the size of
shadowset is same as primary member od
shadowset.

Yes thats pretty normal


Is there any possible way in Alpha-VMS
to combine different sizes of disks in
to one logical disk. When I see the size
of the logical disk, it has to show me
the total size of all the disks in that
logical set.

Yes its possible.
In VMS you can use something called CONCEALED LOGICALS to point to different physical disks. How ever you would still have to shadowcopy those at disk levels.
Let me explain this with a small example

$SH LOG TSTDAT
"TSTDAT" = "DGA1:[TST.DAT]"
= "DGA2:[TST.DAT]"
= "DGA3:[TST.DAT]"
Now DGA1, DGA2 and DGA3 are all independent disks and they need to be shadowcopied at disk level...

Let us know if you have any questions

regards
Mobeen

[Robert Gezelter]

Kiran,

To your first question, the answer is YES, provided you are running at least 7.3-2.

Conceptually, your question of "Why dissimilar volume size?" is a good one. There are two situations in which dissimilar size shadow set members are a significant benefit.

First, there are emergencies. Suppose the only available spare part in an emergency is a larger drive. Dissimilar size device support allows the temporary replacement of a failed shadow set member with a new, albeit wrong (larger) size spare part. When the correct spare is obtained, it can be swapped into the set. Obviously, the system can be running throughout this operation.

Secondly, it presents the possibility for seamless migration to larger disks (and more space, if the initialization parameters were carefully chosen). Consider a shadow set with three 9GB members. Dissimilar device support allows the members to be replaced one at a time with the 18GB members without interrupting system operation.

Dissimilar size shadow sets are not a question of "What good is a dissimilar size volume set on an ongoing basis?" as it is a question of "How do we get from one size shadow set to a larger one without interrupting operations to do the copy?"

I hope that the above is helpful.

- Bob Gezelter, http://www.rlgsc.com

[Robert Gezelter]

Kiran,

My apologies, I hit post before I had completed my answer.

While you cannot combine small disks into a large one for shadowset use, you can create a bound volume set of shadow sets.

Most programs that use very large datasets (e.g., Oracle, RDB) have specific preferences concerning how to expand the data storage area beyond a single volume. These need to be considered before deciding on a storage use strategy.

Bound volume sets are a technique which goes back to the beginnings of OpenVMS, and is very useful. With the advent of larger disks, and more options, older techniques tend to get pushed aside in favor of the latest and greatest. While new techniques are far superior IN SOME CASES, this is not always true.

It is important to look at all the potential solutions, and utilize the best of them in the most parsimonious way, that yields the best result.

- Bob Gezelter, http://www.rlgsc.com

[kiran kumar kolluru]

Thank you for detailed explanations.

Still I have this question.

I created the volume set 'master_pay with

$ mount/bind=master_pay $1$DGA45:,$1$DGA46:,$1$DGA47: test45,test46,test47
%MOUNT-I-MOUNTED, TEST45 mounted on _$1$DGA45: (JETTA)
%MOUNT-I-MOUNTED, TEST46 mounted on _$1$DGA46: (JETTA)
%MOUNT-I-MOUNTED, TEST47 mounted on _$1$DGA47: (JETTA)


$ sh dev $1$dga46

Device Device Error Volume Free Trans Mnt
Name Status Count Label Blocks Count Cnt
$1$DGA45: (JETTA) Mounted alloc 0 TEST45 2096871 1 1
$1$DGA46: (JETTA) Mounted alloc 0 TEST46 2096874 1 1
$1$DGA47: (JETTA) Mounted alloc 0 TEST47 2096874 1 1

Now I believe that I have created a volume set. But my requirement is like If I do '$show dev ' the volume set also to be listed at sys$output (similer to volume shodowing)

-Thanks
Kiran

[Robert Gezelter]

Kiran,

The MFD entries for the volume set are always stored in the MFD of the lead (first) volume in the volume set.

In the situation that you mention, DGA45 would be the lead volume.

As a side note: File IDs actually contain three elements:
- a File Header Number
- the Sequential usage count of that Header (the number of times that the File Header has been recycled)
- a Relative Volume Number

The Relative volume Number is the "glue" that allows Bound Volume Sets to function.

- Bob Gezelter, http://www.rlgsc.com

[Ian Miller. · Accepted solution]

Kiran, you have created a volume set. Note that if one disk fails you lose the volume set (which is why its best to make a volume set out of shadowed disks). Volume sets have various characteristics which you have to note - one of which is the total free space is not displayed - you have to add up the member disks. Also directory files are only created on the first volume in the volume set by default. Files are created on whichever member disk has the most free space at the time of creation.

An alternative is the use if the RAID for OpenVMS Layered product which allows you to create a stripeset out of multiple disks (which may be shadowsets). The stripeset would look like a single disk. This layered product is a extra cost but does work.

[Kris Clippeleyr]

Kiran,


Now I believe that I have created a volume set. But my requirement is like If I do '$show dev ' the volume set also to be listed at sys$output (similer to volume shodowing)


The SHOW DEVICES command displays the status of a device on the system, which basically means 'physical' device, and therefore ignores the bound volume sets. This differs from shadowsets where the system creates a 'virtual' device, e.g. DSA1: which does show up in SHOW DEVICES.

Regards,
Kris (aka Qkcl)

[kiran kumar kolluru]

>>An alternative is the use if the RAID for >>OpenVMS Layered product which allows you >>to create a stripeset out of multiple >>disks (which may be shadowsets). The >>stripeset would look like a single disk. >>This layered product is a extra cost but >>does work.

Yes, It seems I need to look at RAID 0,1,2,3,4,5,3/5 0+1 for this kind of requirement.

Anybody have any pointer to get this layered product.

-thanks
Kiran

[Kris Clippeleyr]

Kiran,

Since you mentioned DGA devices, could it be that you are using a fiber attached disk array. I was thinking about the MSA1000 SAN solution. If this is the case, the MSA1000 has RAID capacity built in.

Regards,
Kris (aka Qkcl)

[John Gillings]

General comment...

As of OpenVMS V7.3-2 you have both dynamic volume expansion and dissimilar size volume shadowing.

In order to make the most of these two features, please make sure you initialise your disks to enable expansion.

For new disks, include the /LIMIT qualifier to your INITIALIZE command. For existing volumes, you need to mount them privately and SET VOLUME/LIMIT.

[Ian Miller.]

Kiran, the RAID Layered product is on the consolidated CD distribtion.
The SPD is
http://h18000.www1.hp.com/info/SP4649/SP4649PF.PDF

some other information is
http://h18000.www1.hp.com/emea/software/uk/storwksraid.html