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Striped datasets

 
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Dudley Millender
Occasional Advisor

Striped datasets

I have a VAX cluster with a VAX8650 and a VAX8550 running VMS 5.5-2. I have 2 RA90 disk drives that I need to create/bind into a striped data set. According to the backup it is looking for a stripe dataset name of HRB. Can you please direct me to the proper documentation or tell me what commands I should do from scratch to build the stripe. The 2 disks are $5$dua9: and $5$dua10:. The reason I need to do this is disk10 crashed and had to be replaced. THANK YOU
13 REPLIES
Hein van den Heuvel
Honored Contributor
Solution

Re: Striped datasets


VMS does not have a native striping solution, where striping is defined as chunks of files alternating between disks.

VMS does support BOUND VOLUME SETS, which present a single starting point, but where files are transparently allocated from multiple drives.
Could is be that you just mean BIND, not STRIPE? If you really mean stripe, then please expaling which tool you were using for that.

If a single disk in a bound set is lost, then you effectivly lost the whole set, allthough it is theoretically possible to 'find' up-to-date, and valid files on the remaining members. But this is likely to be more trouble than it is worth. So you'll need to restore all.

The sequence then becomes something like:

init dua9 data1
init dua10 data2
mount/bind=data dua9:,dua10: data1,data2
backup ...

Check HELP MOUNT and HELP INIT for details.


hth,
Hein.
Lawrence Czlapinski
Trusted Contributor

Re: Striped datasets

Dudley:
1. As Hein said, you might have a BIND set rather than a striped set. A striped set of 2 disks would have 100% of the data from each disk on the other. A striped set of two has no advantages. As Hein said if you lose one disk you lose it all. Even though BIND sets are allowed, personnally, I think they are best avoided. Your data gets spread across disks. Again if you lose one disk of the set, I believe the whole set becomes unavailable since the data is spread across the disks. Generally, for 2 disks you would use shadowing (also called mirroring) rather than striping.
2. A minimum of 3 disks is required for true striping to have a benefit. The data from each disk is spread across the other disks. So the data from disk 1 is also 50% on disk 2 and 50% on disk 3.
3. On VMS, striping is usually done with a RAID (Redundant Array of Independent Disks) Controller. Raid disk names start with DR.
4. From your description, it sounds like you have a BACKUP saveset of HRB.BCK. If that is the case, then the disk volume name is HRB.
Do: $SHOW LOG/SYS DISK*
What are the logical names for $5$DUA9: and $5$DUA10:?
Lawrence
Ian Miller.
Honored Contributor

Re: Striped datasets

To restore a bound volume set from an image backup see
http://h71000.www7.hp.com/wizard/wiz_2581.html
http://h71000.www7.hp.com/wizard/wiz_8948.html
____________________
Purely Personal Opinion
Robert_Boyd
Respected Contributor

Re: Striped datasets

There was a DEC product that I worked with a few years ago that supported host based stripe sets on VMS systems. I don't recall the details at the moment, but it had some similarities to the bound volumeset concept.

I think you might try HELP STRIPE on your system if it is up and running. And do a

SEARCH SYS$SYSROOT:[*...]*.com STRIPE for possible remnants of command procedures that might have been used to initialize the stripeset in the past.

You might GOOGLE VAX VMS STRIPESET too.

Robert
Master you were right about 1 thing -- the negotiations were SHORT!
Robert_Boyd
Respected Contributor

Re: Striped datasets

Here is some online documentation for you

http://www.sysworks.com.au/disk$vaxdocsep002/sysman/d3zkaaa1.p7.bkb#1

Polycenter Striping for OpenVMS VAX

Enjoy,

Robert
Master you were right about 1 thing -- the negotiations were SHORT!
Robert_Boyd
Respected Contributor

Re: Striped datasets

The Polycenter Striping package was later renamed as Compaq Raid. You may find some more recent documentation by looking under that name.

You might also see what you have in your SYS$HELP: directory -- you may have some release notes and possibly even HTML files.

Robert
Master you were right about 1 thing -- the negotiations were SHORT!
Robert Gezelter
Honored Contributor

Re: Striped datasets

Lawrence,

Striping is definitely NOT the same as a Mirror set.

RAID 0 is striping. In effect the logical volume is broken into stripes, and the stripes are alternated between the two physical drives. There is no redundancy inherant in this approach. This gives higher bandwidth performance than is achievable with a single disk.

RAID 1 is mirroring. In RAID 1, each of the disks has a complete copy of the data. It is common to combine mirroring and striping in a configuration referred to as RAID 0/1.

There are other RAID configurations possible, but these are the only ones under this thread.

Bound volume sets, when carefully managed, work very well. Under normal conditions, a given file is kept on a single volume. Files are extended across different volumes when there is an absolute shortage of space.

I hope that the above information is helpful.

- Bob Gezelter, http://www.rlgsc.com
John Gillings
Honored Contributor

Re: Striped datasets

Please don't use bound volume sets. Too old technology with too many dangerous traps you can easily fall into and lose your data.

RA90's? Wow, 9" drives 1.2GB capacity and probably consume the price of a new 100GB disk drive in electricity & aircon every quarter! I guess you must be stuck with them?

If you're really using RAID, the command to create a stripe set is

$ RAID INIT/RAID=0 volname dev1,dev2,...devn

where "volname" is the name of the volume, dev1..devn are the physical devices to be striped. For example:

$ RAID INIT/RAID=0 MYSTRIPE $5$DUA9:,$5$DUA10:

This is a one off operation. BEWARE it will destroy any data on the physical devices.

To use the stripeset, you need to BIND it to a virtual device, DPAnnn: For example:

$ RAID BIND MYSTRIPE $5$DUA9:,$5$DUA10: DPA9:

First time you do this, I think you need to INIT the DPA device:

$ INIT DPA9: MYSRIPE

Finally, you mount the virtual device:

$ MOUNT/CLUSTER DPA9: MYSTRIPE

If you don't have DPA devices on your system, then you're either using 3rd party RAID software, or you're using bound volume sets.
A crucible of informative mistakes
Peter Quodling
Trusted Contributor

Re: Striped datasets

The other thing that might be of relevance here,is what Storage interconnect/hardware you are running. I would assume HSJ40/50? Any idea what version of the software for same you are running?

Q
Leave the Money on the Fridge.
Lawrence Czlapinski
Trusted Contributor

Re: Striped datasets

Robert Gezelter: RAID may allow you to make a striped set of two but it doesn't make any sense to create a striped set of two even if it were allowed. "Generally, for 2 disks you would use shadowing (also called mirroring) rather than striping." I never said striping was the same as shadowing (or mirroring).
Lawrence
Robert_Boyd
Respected Contributor

Re: Striped datasets

Lawrence,

A 2 member stripe set has almost the full capacity of the combined available capacity of the 2 stripeset members. A 2 member shadowset has only the capacity of the smallest of its 2 members available. There are people who use 2 member stripesets -- regardless of whether or not this makes sense from a reliability standpoint.

Personally, I would rather have a combination that is more reliable, like a stripeset of members made up of shadowsets or raid5+3 raidsets for a "plaid" arrangement. I prefer that when using raid to build up multidevice virtual volumes that that they be able to survive the failure of a single physical device and allow for hot replacement of that device.

Robert
Master you were right about 1 thing -- the negotiations were SHORT!
Lawrence Czlapinski
Trusted Contributor

Re: Striped datasets

Robert Gezelter: I assumed that Dudley is running in a Production environment. RAID 0+1 may allow you to make a striped set of two but it doesn't make any sense to create a striped set of two on a Production system even if it were allowed. "Generally, for 2 disks you would use shadowing (also called mirroring) rather than striping." I never said striping was the same as shadowing (or mirroring). We don't use 2 disk striping on development systems either because we often use our development systems as spares for production systems.
Running Raid 0 in a Production environment is a single point failure waiting to happen unless the disks are also shadowed. In this instance there is no indication that the disks are shadowed.
Lawrence
Lawrence Czlapinski
Trusted Contributor

Re: Striped datasets

Robert Gezelter: I strongly agree. I was not precise enough in what I was talking about.
Lawrence