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by sarajane.donahoe

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I am a development manager in an IS shop and am responsible for a SAS application that is running on an HPA UNIX box. We recently did the following and experienced data corruption that caused the application to be down for 1 week. We have yet to get to root cause. I would like to understand if it is a low risk to move data around and add space during working hours or should the server be taken off-line when performing these types of routines?

Work that was done: a physical volume move was done to be able to add storage to the array filesystem. I am told that this needed to be done because of physical limitations within the volume group that contained the array filesystem, and the limitations occured because the array filesystem was never expected to become so large.
Tests were performed on the box w/o errors. Nothing has been found from an application perspective.

Sarajane Donahoe
215-241-2036

5 replies

by shadowofthefallen

Moving data while clients are logged onto the system can cause data corruption (as was seen when I uploaded my website's user database to the site before taking database modifying scripts offline--we corrupted roughly 6000 accounts, 1000 of which were non-recoverable). Modification of files/volumes through a script which locks said files/volumes during its runtime is relatively safe, but transferring data from one location to another is not.

The main problem lies within the fact that clients logged onto the server can modify data as it is being uploaded. A client editing a file stores the file in memory. If a newer version of that file is uploaded to the server, it is overwritten by the older version when the client saves. If a client is running a program which reads from and modifies files on the system, it IS possible for that program to write to random locations in the uploading file and transform its contents to trash.

I would say that it is best if your servers are taken offline before volume transfers occur.

by enserng

Sarajane,

The ultimate size of a database, etcetera is not an easy thing to estimate, and the addition of storage, or increasing the size of a partition should not necessarily be seen as a bad thing. As for accomplishing that task while continuing to allow user access, that is a different matter entirely... Although not necessarily needing to take place after "normal" working hours, all users should be notified, then prohibited access while actually increasing a partitions size or when moving data between partitions or devices. As always, thorough (and periodically tested)incremental and full backups, scheduled to occur at off-peak hours are a MUST have...

Hope this helps,

Nikk

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