[gpfsug-discuss] [EXTERNAL] Intro, and Spectrum Archive self-service recall interface question

[Todd Ruston]

Hi Indulis,

Yes, thanks for the reminder. I'd come across that, and our system is currently set to a stub size of zero (the default, I presume). I'd intended to ask in my original query whether anyone had experimented and found an optimal value that prevents most common inadvertent recalls by Macs. I know that will likely vary by file type, but since we have a broad mix of file types I figure a value that covers the majority of cases without being excessively large is the best we could implement.

Our system is using 16MiB blocks, with 1024 subblocks. Is stub size bounded by full blocks, or subblocks? In other words, would we need to set the stub value to increments of 16MiB, or 16KiB?

Cheers,

- Todd


> On May 21, 2019, at 2:34 AM, Indulis Bernsteins1 <INDULISB at uk.ibm.com> wrote:
> 
> Have you tried looking at Spectrum Archive setting instead of Spectrum Scale? 
> 
> You can set both the size of the "stub file" that remains behind when a file is migrated, and also the amount of data which would need to be read before a recall is triggered. This might catch enough of your recall storms... or at least help! 
> 
> IBM Spectrum Archive Enterprise Edition V1.3.0: Installation and Configuration Guide 
> http://www.redbooks.ibm.com/abstracts/sg248333.html?Open <http://www.redbooks.ibm.com/abstracts/sg248333.html?Open> 
> 
> 7.14.3 Read Starts Recalls: Early trigger for recalling a migrated file 
> IBM Spectrum Archive EE can define a stub size for migrated files so that the stub size initial 
> bytes of a migrated file are kept on disk while the entire file is migrated to tape. The migrated 
> file bytes that are kept on the disk are called the stub. Reading from the stub does not trigger 
> a recall of the rest of the file. After the file is read beyond the stub, the recall is triggered. The 
> recall might take a long time while the entire file is read from tape because a tape mount 
> might be required, and it takes time to position the tape before data can be recalled from tape. 
> When Read Start Recalls (RSR) is enabled for a file, the first read from the stub file triggers a 
> recall of the complete file in the background (asynchronous). Reads from the stubs are still 
> possible while the rest of the file is being recalled. After the rest of the file is recalled to disks, 
> reads from any file part are possible. 
> With the Preview Size (PS) value, a preview size can be set to define the initial file part size 
> for which any reads from the resident file part does not trigger a recall. Typically, the PS value 
> is large enough to see whether a recall of the rest of the file is required without triggering a 
> recall for reading from every stub. This process is important to prevent unintended massive 
> recalls. The PS value can be set only smaller than or equal to the stub size. 
> This feature is useful, for example, when playing migrated video files. While the initial stub 
> size part of a video file is played, the rest of the video file can be recalled to prevent a pause 
> when it plays beyond the stub size. You must set the stub size and preview size to be large 
> enough to buffer the time that is required to recall the file from tape without triggering recall 
> storms. 
> Use the following dsmmigfs command options to set both the stub size and preview size of 
> the file system being managed by IBM Spectrum Archive EE: 
> dsmmigfs Update -STUBsize 
> dsmmigfs Update -PREViewsize 
> The value for the STUBsize is a multiple of the IBM Spectrum Scale file system’s block size. 
> this value can be obtained by running the mmlsfs <filesystem>. The PREViewsize parameter 
> must be equal to or less than the STUBsize value. Both parameters take a positive integer in 
> bytes.
> 
>  Regards,
>   
> Indulis Bernsteins
> Systems Architect
> IBM New Generation Storage 
> Phone: +44 792 008 6548
> E-mail: INDULISB at UK.IBM.COM	
> 
> 
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