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Re: Exercising the Disk

 
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SAKET_5
Honored Contributor

Exercising the Disk

Hi All,

may be a simple one for some of you...

whats the idea behind exercising the disk, i.e. either via SSSU on EVAs - Exercise disk command or on HSG80 utility DILX?

any recommendations here?

just curious for info...

regards,
9 REPLIES 9
Uwe Zessin
Honored Contributor

Re: Exercising the Disk

It is used for stress-testing (things more likely fail under high loads) and for verification. You can test the disks and back-end interconnects without any servers attached.
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B. Hulst
Trusted Contributor

Re: Exercising the Disk

Hi,

For exercising a disk under unix you can also
do this command a few times:

dd if=/dev/dsk/c4t3d0 of=/dev/null

It will read the complete device and write the output into the unix /dev/null device.

Regards,
Bob

Uwe Zessin
Honored Contributor

Re: Exercising the Disk

There is a comment in the EVA's documentation that this might not do what you expect from the EVA, because this system tracks which blocks have been written and will not return data that you have not written previously.

If you do that on a newly created virtual disk, the EVA will not go to the physical disk - it will 'invent' data and return this to your server.
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Nguyen Anh Tien
Honored Contributor

Re: Exercising the Disk

Hi Saket.
I have no exercises for disk. but you can get EVA emulator at

http://www.magirus.com/germany/hardware/hp/news/news_08557.php
HP is simple
Uwe Zessin
Honored Contributor

Re: Exercising the Disk

This is not a question about EVA training :-)

We're talking about an EXERCISER - that is a functional test program for hard/software.
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SAKET_5
Honored Contributor

Re: Exercising the Disk

Uwe,

on the HSG's is there any such recommendations to run DILX on new disks before you insert them or does running DILX affect all the disks?

I have an old HSG80 based SA that has not been used in a while...i configured it the other day and i see a few disks failing every now and them especially when I need to create any raidsets and perform an init...they fail...i was thinking of running a thorough DILX to see if i can detect all the disks that are in their pre-dictive failure state...

does running DILX affect any existing configurations...i know it can delete some stuff...like...the EISA partitions, etc...

also, another one for you...whats the idea of making a disk "transportable" on HSG80s? We have got an old box running SCO UNIX...and one of its mirrored disks died...now any attempt to replace the failed disk with a working one - just wont let the mirror rebuild....so i ve been suggested to plug this disk into our HSG80s and make it transportable to see if there are any *malicious* metadata - which can be cleared....lil confused...

thanks
Uwe Zessin
Honored Contributor

Re: Exercising the Disk

DILX does not operate on physical disks - it operates on units. But you can create a single-disk unit and then run DILX on it ;-)


I would individually INITIALIZE the physical members, e.g.:

> INIT DISK10000
> INIT DISK20000

and then create the storage set like:

> ADD MIRROR M1 DISK10000 DISK20000
> INIT M1

as I have found that sometimes the storage set INIT can fail even if the disks are fine. If a single physical disk fails the INIT - throw it away or better sell it so somebody else has some fun, too ;-)


You need to be very careful not to DILX the wrong units in write mode, obviously. But as far as I am aware, the HSG80 cannot deal with predictive failure warnings - a disk in a HSG-based storage system is not covered by a pre-failure warranty :-(


"TRANSPORTABLE" means that a disk has no space reserved for meta-data. Assume you have a single disk sticking in a server on a simple SCSI adapter (no backplane RAID). You can:
- remove the disk from this server
- 'transport' it to the HSG-based storage
- plug it in
- add the disk entry
- set it to "TRANSPORTABLE"
- put a unit on top of it

The disk with all data is now presented 'as-is'. You can mount it on a different server attached to the SAN and transfer the data to a different unit. Or you can put data _on_ the "TRANSPORTABLE" disk to make it available for the server that has no SAN attach. It could be, for example, a system disk from a server that does not even have a tape drive for backup/restore. It can be useful for _many_ things.


Indeed you can 'abuse' the "TRANSPORTABLE" setting to make all blocks accessible for a different server and, perhaps, erase the whole disk to get rid of a backplane RAID controller's meta-data (clever idea).
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SAKET_5
Honored Contributor

Re: Exercising the Disk

Uwe,

you legend! thanks for your great response:)

a question tho...in my scenario..where if i move the drive that refuses to rebuild the mirror on this old SCO UNIX box, if i take it and plug it into the HSG80 array...set it to transportable (i still have to figure out exactly which command...guessing something like set unit_name transportable or can we do it on individual disk?...)..does this mean...the HSG80s write their own metadata at this stage and set it so that this disk can be moved to another raid card - or another HSG80s and this metadata can not be modified? does it also mean that the HSG80 will erase any existing metadata or erase the whole disk when setting it to be "transportable"?

when i take this disk to connect back into the server's local raid card, after being configured as "transportable" by the HSG80s, does this mean that the server's raid controller wont be able to write its own metadata on this disk?

sorry...never had to get involved in this...may be askin some of the silly ones now...but its also too late n may be i should just hit the bed...

once again..thanks for your great support...

regards,





Uwe Zessin
Honored Contributor
Solution

Re: Exercising the Disk

"TRANSPORTABLE" is a characteristic of an individual disk drive:

> ADD DISK DISK10400 1 4 0 TRANSPORTABLE
? don't recall if "INIT DISK10400" is necessary, here
> ADD UNIT D1 DISK10400 DISABLE_ACCESS_PATH=ALL

"TRANSPORTABLE" is just a means to tell the HSG to present the whole data area of the disk to a server, unaltered. Once a disk has been set "TRANSPORTABLE", there is simply no room for *ACS* meta-data (see below). This command will not touch the user's data, another controller's meta-data or even ERASE the whole disk! If it did overwrite anything, you could not safely get at the old data on the disk to 'import' it into the storage system (via file copy - don't take 'import' literally).

You can safely pull a "TRANSPORTABLE" disk from a HSG-based storage and use it somewhere else. I would even set disks 'back' to TRANSPORTABLE if I would use disks that had been part of a storage set.


Try this on a scratch disk:

> ADD DISK DISK10400 1 4 0
> INIT DISK10400
> SHOW DISK10400
> SET DISK10400 TRANSPORTABLE
> SHOW DISK10400

and see how the size changes. Once you have given an "INIT" command, it means that meta-data has been written and _some_ old data is gone! It also means that the HSG has altered one of the disk's SCSI mode pages so that it appears as a smaller disk. The "INIT" command does not erase the whole disk - look how fast it goes!


Different controllers have different ideas of where to store their meta-data. The HSG puts it at the end of the disk (after the newly reported size). Some other controller can put it at the beginning of the disk.


(Hope you have slept well and I have addressed all questions. I understand this is not an easy topic.)
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