Hi Serkan,
I think the problem is in the temporary name that distcp gives to the
file while it's being copied before renaming it to the real name. Do you
know what is the structure of this name ?
DHT selects the subvolume (in this case the ec set) on which the file
will be stored based on the name of the file. This has a problem when a
file is being renamed, because this could change the subvolume where the
file should be found.
DHT has a feature to avoid incorrect file placements when executing
renames for the rsync case. What it does is to check if the file matches
the following regular expression:
^\.(.+)\.[^.]+$
If a match is found, it only considers the part between parenthesis to
calculate the destination subvolume.
This is useful for rsync because temporary file names are constructed in
the following way: suppose the original filename is 'test'. The
temporary filename while rsync is being executed is made by prepending a
dot and appending '.<random chars>': .test.712hd
As you can see, the original name and the part of the name between
parenthesis that matches the regular expression are the same. This
causes that, after renaming the temporary file to its original filename,
both files will be considered to belong to the same subvolume by DHT.
In your case it's very probable that distcp uses a temporary name like
'.part.<number>'. In this case the portion of the name used to select
the subvolume is always 'part'. This would explain why all files go to
the same subvolume. Once the file is renamed to another name, DHT
realizes that it should go to another subvolume. At this point it
creates a link file (those files with access rights = '---------T') in
the correct subvolume but it doesn't move it. As you can see, this kind
of files are better balanced.
To solve this problem you have three options:
1. change the temporary filename used by distcp to correctly match the
regular expression. I'm not sure if this can be configured, but if this
is possible, this is the best option.
2. define the option 'extra-hash-regex' to an expression that matches
your temporary file names and returns the same name that will finally
have. Depending on the differences between original and temporary file
names, this option could be useless.
3. set the option 'rsync-hash-regex' to 'none'. This will prevent the
name conversion, so the files will be evenly distributed. However this
will cause a lot of files placed in incorrect subvolumes, creating a lot
of link files until a rebalance is executed.
Xavi
On 20/04/16 14:13, Serkan Çoban wrote:
Here is the steps that I do in detail and relevant output from bricks:
I am using below command for volume creation:
gluster volume create v0 disperse 20 redundancy 4 \
1.1.1.{185..204}:/bricks/02 \
1.1.1.{205..224}:/bricks/02 \
1.1.1.{225..244}:/bricks/02 \
1.1.1.{185..204}:/bricks/03 \
1.1.1.{205..224}:/bricks/03 \
1.1.1.{225..244}:/bricks/03 \
1.1.1.{185..204}:/bricks/04 \
1.1.1.{205..224}:/bricks/04 \
1.1.1.{225..244}:/bricks/04 \
1.1.1.{185..204}:/bricks/05 \
1.1.1.{205..224}:/bricks/05 \
1.1.1.{225..244}:/bricks/05 \
1.1.1.{185..204}:/bricks/06 \
1.1.1.{205..224}:/bricks/06 \
1.1.1.{225..244}:/bricks/06 \
1.1.1.{185..204}:/bricks/07 \
1.1.1.{205..224}:/bricks/07 \
1.1.1.{225..244}:/bricks/07 \
1.1.1.{185..204}:/bricks/08 \
1.1.1.{205..224}:/bricks/08 \
1.1.1.{225..244}:/bricks/08 \
1.1.1.{185..204}:/bricks/09 \
1.1.1.{205..224}:/bricks/09 \
1.1.1.{225..244}:/bricks/09 \
1.1.1.{185..204}:/bricks/10 \
1.1.1.{205..224}:/bricks/10 \
1.1.1.{225..244}:/bricks/10 \
1.1.1.{185..204}:/bricks/11 \
1.1.1.{205..224}:/bricks/11 \
1.1.1.{225..244}:/bricks/11 \
1.1.1.{185..204}:/bricks/12 \
1.1.1.{205..224}:/bricks/12 \
1.1.1.{225..244}:/bricks/12 \
1.1.1.{185..204}:/bricks/13 \
1.1.1.{205..224}:/bricks/13 \
1.1.1.{225..244}:/bricks/13 \
1.1.1.{185..204}:/bricks/14 \
1.1.1.{205..224}:/bricks/14 \
1.1.1.{225..244}:/bricks/14 \
1.1.1.{185..204}:/bricks/15 \
1.1.1.{205..224}:/bricks/15 \
1.1.1.{225..244}:/bricks/15 \
1.1.1.{185..204}:/bricks/16 \
1.1.1.{205..224}:/bricks/16 \
1.1.1.{225..244}:/bricks/16 \
1.1.1.{185..204}:/bricks/17 \
1.1.1.{205..224}:/bricks/17 \
1.1.1.{225..244}:/bricks/17 \
1.1.1.{185..204}:/bricks/18 \
1.1.1.{205..224}:/bricks/18 \
1.1.1.{225..244}:/bricks/18 \
1.1.1.{185..204}:/bricks/19 \
1.1.1.{205..224}:/bricks/19 \
1.1.1.{225..244}:/bricks/19 \
1.1.1.{185..204}:/bricks/20 \
1.1.1.{205..224}:/bricks/20 \
1.1.1.{225..244}:/bricks/20 \
1.1.1.{185..204}:/bricks/21 \
1.1.1.{205..224}:/bricks/21 \
1.1.1.{225..244}:/bricks/21 \
1.1.1.{185..204}:/bricks/22 \
1.1.1.{205..224}:/bricks/22 \
1.1.1.{225..244}:/bricks/22 \
1.1.1.{185..204}:/bricks/23 \
1.1.1.{205..224}:/bricks/23 \
1.1.1.{225..244}:/bricks/23 \
1.1.1.{185..204}:/bricks/24 \
1.1.1.{205..224}:/bricks/24 \
1.1.1.{225..244}:/bricks/24 \
1.1.1.{185..204}:/bricks/25 \
1.1.1.{205..224}:/bricks/25 \
1.1.1.{225..244}:/bricks/25 \
1.1.1.{185..204}:/bricks/26 \
1.1.1.{205..224}:/bricks/26 \
1.1.1.{225..244}:/bricks/26 \
1.1.1.{185..204}:/bricks/27 \
1.1.1.{205..224}:/bricks/27 \
1.1.1.{225..244}:/bricks/27 force
then I mount volume on 50 clients:
mount -t glusterfs 1.1.1.185:/v0 /mnt/gluster
then I make a directory from one of the clients and chmod it.
mkdir /mnt/gluster/s1 && chmod 777 /mnt/gluster/s1
then I start distcp on clients, there are 1059X8.8GB files in one folder and
they will be copied to /mnt/gluster/s1 with 100 parallel which means 2
copy jobs per client at same time.
hadoop distcp -m 100 http://nn1:8020/path/to/teragen-10tb file:///mnt/gluster/s1
After job finished here is the status of s1 directory from bricks:
s1 directory is present in all 1560 brick.
s1/teragen-10tb folder is present in all 1560 brick.
full listing of files in bricks:
https://www.dropbox.com/s/rbgdxmrtwz8oya8/teragen_list.zip?dl=0
You can ignore the .crc files in the brick output above, they are
checksum files...
As you can see part-m-xxxx files written only some bricks in nodes 0205..0224
All bricks have some files but they have zero size.
I increase file descriptors to 65k so it is not the issue...
On Wed, Apr 20, 2016 at 9:34 AM, Xavier Hernandez <xhernandez@xxxxxxxxxx> wrote:
Hi Serkan,
On 19/04/16 15:16, Serkan Çoban wrote:
I assume that gluster is used to store the intermediate files before
the reduce phase
Nope, gluster is the destination for distcp command. hadoop distcp -m
50 http://nn1:8020/path/to/folder file:///mnt/gluster
This run maps on datanodes which have /mnt/gluster mounted on all of them.
I don't know hadoop, so I'm of little help here. However it seems that -m 50
means to execute 50 copies in parallel. This means that even if the
distribution worked fine, at most 50 (much probably less) of the 78 ec sets
would be used in parallel.
This means that this is caused by some peculiarity of the mapreduce.
Yes but how a client write 500 files to gluster mount and those file
just written only to subset of subvolumes? I cannot use gluster as a
backup cluster if I cannot write with distcp.
All 500 files were created only on one of the 78 ec sets and the remaining
77 got empty ?
You should look which files are created in each brick and how many
while the process is running.
Files only created on nodes 185..204 or 205..224 or 225..244. Only on
20 nodes in each test.
How many files there were in each brick ?
Not sure if this can be related, but standard linux distributions have a
default limit of 1024 open file descriptors. Having a so big volume and
doing a massive copy, maybe this limit is affecting something ?
Are there any error or warning messages in the mount or bricks logs ?
Xavi
On Tue, Apr 19, 2016 at 1:05 PM, Xavier Hernandez <xhernandez@xxxxxxxxxx>
wrote:
Hi Serkan,
moved to gluster-users since this doesn't belong to devel list.
On 19/04/16 11:24, Serkan Çoban wrote:
I am copying 10.000 files to gluster volume using mapreduce on
clients. Each map process took one file at a time and copy it to
gluster volume.
I assume that gluster is used to store the intermediate files before the
reduce phase.
My disperse volume consist of 78 subvolumes of 16+4 disk each. So If I
copy >78 files parallel I expect each file goes to different subvolume
right?
If you only copy 78 files, most probably you will get some subvolume
empty
and some other with more than one or two files. It's not an exact
distribution, it's a statistially balanced distribution: over time and
with
enough files, each brick will contain an amount of files in the same
order
of magnitude, but they won't have the *same* number of files.
In my tests during tests with fio I can see every file goes to
different subvolume, but when I start mapreduce process from clients
only 78/3=26 subvolumes used for writing files.
This means that this is caused by some peculiarity of the mapreduce.
I see that clearly from network traffic. Mapreduce on client side can
be run multi thread. I tested with 1-5-10 threads on each client but
every time only 26 subvolumes used.
How can I debug the issue further?
You should look which files are created in each brick and how many while
the
process is running.
Xavi
On Tue, Apr 19, 2016 at 11:22 AM, Xavier Hernandez
<xhernandez@xxxxxxxxxx> wrote:
Hi Serkan,
On 19/04/16 09:18, Serkan Çoban wrote:
Hi, I just reinstalled fresh 3.7.11 and I am seeing the same behavior.
50 clients copying part-0-xxxx named files using mapreduce to gluster
using one thread per server and they are using only 20 servers out of
60. On the other hand fio tests use all the servers. Anything I can do
to solve the issue?
Distribution of files to ec sets is done by dht. In theory if you
create
many files each ec set will receive the same amount of files. However
when
the number of files is small enough, statistics can fail.
Not sure what you are doing exactly, but a mapreduce procedure
generally
only creates a single output. In that case it makes sense that only one
ec
set is used. If you want to use all ec sets for a single file, you
should
enable sharding (I haven't tested that) or split the result in multiple
files.
Xavi
Thanks,
Serkan
---------- Forwarded message ----------
From: Serkan Çoban <cobanserkan@xxxxxxxxx>
Date: Mon, Apr 18, 2016 at 2:39 PM
Subject: disperse volume file to subvolume mapping
To: Gluster Users <gluster-users@xxxxxxxxxxx>
Hi, I have a problem where clients are using only 1/3 of nodes in
disperse volume for writing.
I am testing from 50 clients using 1 to 10 threads with file names
part-0-xxxx.
What I see is clients only use 20 nodes for writing. How is the file
name to sub volume hashing is done? Is this related to file names are
similar?
My cluster is 3.7.10 with 60 nodes each has 26 disks. Disperse volume
is 78 x (16+4). Only 26 out of 78 sub volumes used during writes..
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