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тАО04-23-2006 12:27 AM
тАО04-23-2006 12:27 AM
Re: Disk Cluster Size too Large
In essence, Hein is correct. A while ago, a systems programmer at a site with which I was connected throught that the correct allocation minimum would be half a disk track (in those days approximately ten sectors).
When disk space ran low, an analyis showed that our actual file allocations were resulting in a breakage factor of approximately 30% (30% of our disk space was unusable because of the "last sector vs. last allocated sector" effect (a one block file used only a single block but allocated an entire cluster).
A secondary problem was backup capabilities (or lack thereof). Pre-BACKUP, there was no good tool to restoring a disk with a different cluster factor.
The option of simply purchasing an additional disk drive was out of the question. Then current prices meant that that option was, in relative terms, the equivalent of a good portion of a man-year, and totally out of the question.
Researching the problem, I was able to determine (for an ODS-2 disk) the necessary surgery was feasible. Ensuring that the data was backed up, I dismounted the disk, and sucessfully made the changes. (I was also not a cowboy about it, I did take the precaution of checking with one of my Engineering contacts, Hein can take a good guess as to whom, but I will not identify). My contact noted that there was an even shorter way to accomplish what I was doing.
Was it the computer equivalent of neurosurgery, probably. But neurosurgery is reasonably safe, when done with the correct preparation, testing, and care.
Would I (and could I) do it again in the same or a similar situation, yes. Do I recommend it as a general procedure, NO. The actual downtime to do this change is measured in seconds, and does not require a reboot of the system or cluster. Properly prepared, the operation is safe.
- Bob Gezelter, http://www.rlgsc.com
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тАО04-23-2006 10:32 AM
тАО04-23-2006 10:32 AM
Re: Disk Cluster Size too Large
I unmount the raid array and then set the cluster size without reinitializing it - correct?
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тАО04-23-2006 12:40 PM
тАО04-23-2006 12:40 PM
Re: Disk Cluster Size too Large
It is not that simple.
I said that it can be accomplished in that time scale, but while I would do it in appropriate situations, it is a delicate operation, not just a question of issuing one or two easy commands.
- Bob Gezelter, http://www.rlgsc.com
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тАО04-23-2006 12:45 PM
тАО04-23-2006 12:45 PM
Re: Disk Cluster Size too Large
I hit "Submit" too quickly.
With the proper preparation, the actual switch of the cluster factor is a fairly fast operation (the switch would in today's technologies, would be very short).
However, I want to be clear (if for nothing else, the future readers of this discussion). While the operation can be done quickly, it is not merely a question of issuing a DISMOUNT, one or two standard commands, and then re-MOUNTing the volumes.
- Bob Gezelter, http://www.rlgsc.com
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тАО04-24-2006 01:53 AM
тАО04-24-2006 01:53 AM
Re: Disk Cluster Size too Large
Next question, when I backup the data back to these re-init'd disks with the new cluster size, is there going to be a problem because of the difference in cluster size?
And, what exactly is the best cluster size I should re-init them to?
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тАО04-24-2006 01:58 AM
тАО04-24-2006 01:58 AM
Re: Disk Cluster Size too Large
be sure to make the backup with BACKUP/IMAGE... and the restore with BACKUP/IMAGE/NOINIT..., else the restore would reinit the disk with its original settings.
The clustersize should be selecting with respect to the size of the files being stored on the disk. If you have a lot of small files, setting a big clustersize would waste a lot of space, while big files allow for bigger clustersizes.
If the 'typical' file fits in one cluster, it will always be contigous.
regards Kalle
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тАО04-24-2006 02:03 AM
тАО04-24-2006 02:03 AM
Re: Disk Cluster Size too Large
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тАО04-24-2006 02:17 AM
тАО04-24-2006 02:17 AM
Re: Disk Cluster Size too Large
(smile) You have seen too many wildcards! (Smile) 2*2*7*7*7 is also expressible as:
(2**2)*(7**3)
In other words, the "*" are arithmetic operators, not wildcards. So, for example, cluster factors of 2, 4, 7, 14,... would all be valid if you were restructuring the volume.
If you are re-initializing the volumes, this is not a concern, any cluster factor is acceptable (although depending precisely on what disks and controllers you have, some may be better than others).
If the copying is a roadblock, as I said, the conversion can be done, albeit with care. If you wish, I will be happy to speak offline with you about it.
I hope that the preceeding is helpful.
- Bob Gezelter, http://www.rlgsc.com
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тАО04-24-2006 02:42 AM
тАО04-24-2006 02:42 AM
Re: Disk Cluster Size too Large
What's this called in english?
- prime factorization ?
- prime decomposition ?
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тАО04-24-2006 03:00 AM
тАО04-24-2006 03:00 AM
Re: Disk Cluster Size too Large
In English, Prime Factorization.
Not that we notice it often, but there is an ambiguity in notation (the WildCard Pattern Matching syntax vs. Mathematics).
While I have not often fallen into that trap, overloaded syntax is always a potential source of mis-understandings.
- Bob Gezelter, http://www.rlgsc.com