zfs discuss - Mar 2007 - Is there any performance problem with hard links in ZFS?

Is there any performance problem with hard  links in ZFS?
I have a large storage. There will be near 50000 hard links for every file.  Is
it ok for ZFS? May be some problems with  snapshots(every 30 minutes there will
be a snapshot creating)?  What about difference in speed while working with
50000 hardlinks or 50000 different files?

ps: It would be very useful if you give me some links about hardlinks low-level
processing.
 
 
This message posted from opensolaris.org

Viktor Turskyi wrote:
> Is there any performance problem with hard  links in ZFS?
> I have a large storage. There will be near 50000 hard links for every file.
Is it ok for ZFS? May be some problems with  snapshots(every 30 minutes there
will be a snapshot creating)?  What about difference in speed while working with
50000 hardlinks or 50000 different files?
Why do you think there would be a problem ?

Are you actually having a problem or trying to guess at things you might 
have ?

To my knowledge there are no problems with hard or softlinks in ZFS.

50000 hard links for a file seems very strange and it really sounds like 
what you might want is to use ZFS clones.  What problem are you solving 
by using such a huge number of hardlinks ?
> ps: It would be very useful if you give me some links about hardlinks
low-level processing.
Look in the zfs community page on opensolaris.org

-- 
Darren J Moffat

Viktor Turskyi wrote:
> Is there any performance problem with hard  links in ZFS?
> I have a large storage. There will be near 50000 hard links for every file.
Is it ok for ZFS? May be some problems with  snapshots(every 30 minutes there
will be a snapshot creating)?  What about difference in speed while working with
50000 hardlinks or 50000 different files?
> 
> ps: It would be very useful if you give me some links about hardlinks
low-level processing.
>  
>  
> This message posted from opensolaris.org

On my 2 Ghz opteron w/ 2 mirrored zfs disks:


cyber% cat test.c
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>

int
main(int argc, char *argv[])
{
         int i;
         char *filename;
         char buffer[1024];

         if (argc != 2) {
                 fprintf(stderr, "usage: %s filename\n", argv[0]);
                 exit(1);
         }

         strcpy(buffer, argv[1]);
         filename = buffer + strlen(filename);

         for (i = 0; i < 50000; i++) {
                 sprintf(filename, "_%d\n", i);
                 if(link("foo",  buffer) < 0) {
                         perror("link:");
                         exit(1);
                 }
         }
}

cyber% ls
test    test.c
cyber% cc -o test test.c
cyber% mkfile 10k foo
cyber% /bin/ptime ./test foo

real        0.976
user        0.039
sys         0.936
cyber% ls | wc
   100003   50003  538906
cyber% /bin/ptime rm foo_*

real        1.869
user        0.110
sys         1.757
cyber%

So it takes just under 1 second to create 50,000 hardlinks to a file; it 
takes just under 2 seconds to delete ''em w/ rm.  It would prob. be 
faster to use a program to delete them.

- Bart


-- 
Bart Smaalders			Solaris Kernel Performance
barts at cyber.eng.sun.com		http://blogs.sun.com/barts

Viktor Turskyi wrote:
> Is there any performance problem with hard  links in ZFS? I have a
> large storage. There will be near 50000 hard links for every file.
> Is it ok for ZFS? May be some problems with  snapshots(every 30
> minutes there will be a snapshot creating)?  What about difference in
> speed while working with 50000 hardlinks or 50000 different files?
> 
> ps: It would be very useful if you give me some links about hardlinks
> low-level processing.
Hard links in ZFS work pretty much the same as in any other UNIX 
filesystem -- which is to say, they are very fast.  Should be much much 
faster than the same number of different files.

--matt

Thank you very much for the consultation. The information was very useful. 

And I have one more questions about ZFS file attributes. I have found such
information "2^56 ? Number of attributes of a file in ZFS" but i cant
found any information mechanism of creating such attributes.  The situation is
next: I want to save a lot of file information not in database but in file
attributes. File attributes setting will be processing by a Perl or C program.
Is there any way to do this?
 
 
This message posted from opensolaris.org

Viktor Turskyi wrote:
> Thank you very much for the consultation. The information was very
> useful.
You''re welcome!
> And I have one more questions about ZFS file attributes. I have found
> such information "2^56 ? Number of attributes of a file in ZFS"
but i
> cant found any information mechanism of creating such attributes.
> The situation is next: I want to save a lot of file information not
> in database but in file attributes. File attributes setting will be
> processing by a Perl or C program. Is there any way to do this?
See fsattr(5)

--matt

>See fsattr(5) 
It was helpful :). Thanks!
 
 
This message posted from opensolaris.org

i have tested links performance. and i have got such results:
with hardlinks - no problems, reading of 50000 files one million times takes 38
seconds
in case with symlinks is another situation - reading of 50000 files(through
symlinks) one million times takes 3,5 minutes.
Is this OK? Is it normal that symlinks in so many times slower than hardlinks?
 
 
This message posted from opensolaris.org

On Mon, 26 Mar 2007, Viktor Turskyi wrote:
> i have tested links performance. and i have got such results:
> with hardlinks - no problems, reading of 50000 files one million times
takes 38 seconds
> in case with symlinks is another situation - reading of 50000 files(through
symlinks) one million times takes 3,5 minutes.
> Is this OK? Is it normal that symlinks in so many times slower than
hardlinks?
Tested this on UFS or on ZFS ?
How long were the filenames of the links ?

FrankH.