ZFS actually uses the ZAP to handle directory lookups. The ZAP is
not a btree but a specialized hash table where a hash for each
directory entry is generated based on that entry's name. Hence you
won't be doing any sort of linear search through the entire directory
for a file, a hash is generated from the file name and a lookup of
that hash in the zap will be done. This is nice and speedy, even
with 100,000 files in a directory.
Noel
On Aug 24, 2006, at 8:02 AM, Patrick Narkinsky wrote:
Due to legacy constraints, I have a rather complicated system that
is currently using Sun QFS (actually the SAM portion of it.) For a
lot of reasons, I'd like to look at moving to ZFS, but would like a
"sanity check" to make sure ZFS is suitable to this application.
First of all, we are NOT using the cluster capabilities of SAMFS.
Instead, we're using it as a way of dealing with one directory that
contains approximately 100,000 entries.
The question is this: I know from the specs that ZFS can handle a
directory with this many entries, but what I'm actually wondering
is how directory lookups are handled? That is, if I do a "cd
foo050000" in a directory with foo000001 through foo100000, will
the filesystem have to scroll through all the directory contents to
find foo050000, or does it use a btree or something to handle this?
This directory is, in turn, shared out over NFS. Are there any
issues I should be aware of with this sort of installation?
Thanks for any advice or input!
Patrick Narkinsky
Sr. System Engineer
EDS
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