What is the meaning of "recall storms" in vfs_gpfs.8?

Michael Adam obnox at samba.org
Mon Mar 28 08:18:40 UTC 2016

On 2016-03-28 at 16:11 +0900, Samba-JP oota wrote:
> In Samba 4.2.0 vfs_gpfs.8 document,
> Some phrases were added like this.
> <para> When this option is set to no, an attempt to
>        open an offline file will be rejected with access
>        denied.  This helps preventing recall storms triggered
>                                       -------------
>        by careless applications like Finder and
>        Explorer.</para>
> What kind of meaning is "recall storms" in this phrase?
> Is Explorer to perform re-reading of a file repeatedly?

Recall is the process of getting files back from tape
(or other slower tier in the HSM) back to the faster
front tier.

The storm refers to _many_ files being recalled more or
less simultaneously, triggered by certain actions of
explorer (etc).

The problem here is that the explorer always reads the
first few bytes of a file which is not flagged offline
in order to get the icon, etc. So the non-offline files
in the folder need to be recalled for listing.

Hence it is not necessary to read files repeatedly in
order to recall _many_ files (create a recall storm):
Just displaying a directory with a lot of files will do it.

Hope this makes it more clear!

Cheers - Michael
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