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<div class="moz-cite-prefix">On 04/27/2015 01:52 PM, Ben Turner
wrote:<br>
</div>
<blockquote
cite="mid:357725768.6011704.1430167955312.JavaMail.zimbra@redhat.com"
type="cite">
<pre wrap="">----- Original Message -----
</pre>
<blockquote type="cite">
<pre wrap="">From: "Ernie Dunbar" <a class="moz-txt-link-rfc2396E" href="mailto:maillist@lightspeed.ca"><maillist@lightspeed.ca></a>
To: "Gluster Users" <a class="moz-txt-link-rfc2396E" href="mailto:gluster-users@gluster.org"><gluster-users@gluster.org></a>
Sent: Monday, April 27, 2015 4:24:56 PM
Subject: Re: [Gluster-users] Disastrous performance with rsync to mounted Gluster volume.
On 2015-04-24 11:43, Joe Julian wrote:
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">This should get you where you need to be. Before you start to migrate
the data maybe do a couple DDs and send me the output so we can get an
idea of how your cluster performs:
time `dd if=/dev/zero of=<gluster-mount>/myfile bs=1024k count=1000;
sync`
echo 3 > /proc/sys/vm/drop_caches
dd if=<gluster mount> of=/dev/null bs=1024k count=1000
If you are using gigabit and glusterfs mounts with replica 2 you
should get ~55 MB / sec writes and ~110 MB / sec reads. With NFS you
will take a bit of a hit since NFS doesnt know where files live like
glusterfs does.
</pre>
</blockquote>
</blockquote>
<pre wrap="">
After copying our data and doing a couple of very slow rsyncs, I did
your speed test and came back with these results:
1048576 bytes (1.0 MB) copied, 0.0307951 s, 34.1 MB/s
root@backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
count=1024 bs=1024; sync
1024+0 records in
1024+0 records out
1048576 bytes (1.0 MB) copied, 0.0298592 s, 35.1 MB/s
root@backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
count=1024 bs=1024; sync
1024+0 records in
1024+0 records out
1048576 bytes (1.0 MB) copied, 0.0501495 s, 20.9 MB/s
root@backup:/home/webmailbak# echo 3 > /proc/sys/vm/drop_caches
root@backup:/home/webmailbak# # dd if=/mnt/testfile of=/dev/null
bs=1024k count=1000
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.0124498 s, 84.2 MB/s
Keep in mind that this is an NFS share over the network.
I've also noticed that if I increase the count of those writes, the
transfer speed increases as well:
2097152 bytes (2.1 MB) copied, 0.036291 s, 57.8 MB/s
root@backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
count=2048 bs=1024; sync
2048+0 records in
2048+0 records out
2097152 bytes (2.1 MB) copied, 0.0362724 s, 57.8 MB/s
root@backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
count=2048 bs=1024; sync
2048+0 records in
2048+0 records out
2097152 bytes (2.1 MB) copied, 0.0360319 s, 58.2 MB/s
root@backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
count=10240 bs=1024; sync
10240+0 records in
10240+0 records out
10485760 bytes (10 MB) copied, 0.127219 s, 82.4 MB/s
root@backup:/home/webmailbak# dd if=/dev/zero of=/mnt/testfile
count=10240 bs=1024; sync
10240+0 records in
10240+0 records out
10485760 bytes (10 MB) copied, 0.128671 s, 81.5 MB/s
</pre>
</blockquote>
<pre wrap="">
This is correct, there is overhead that happens <strike>with small files and</strike> the smaller the file the less throughput you get. That said, since files are smaller you should get more files / second but less MB / second. I have found that when you go under 16k changing files size doesn't matter, you will get the same number of 16k files / second as you do 1 k files.</pre>
</blockquote>
<br>
The overhead happens regardless. You just notice it more when you're
doing it a lot more frequently.<br>
<br>
<blockquote
cite="mid:357725768.6011704.1430167955312.JavaMail.zimbra@redhat.com"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">
However, the biggest stumbling block for rsync seems to be changes to
directories. I'm unsure about what exactly it's doing (probably changing
last access times?) but these minor writes seem to take a very long time
when normally they would not. Actual file copies (as in the very files
that are actually new within those same directories) appear to take
quite a lot less time than the directory updates.
</pre>
</blockquote>
<pre wrap="">
Dragons be here! Access time is not kept in sync across the replicas(IIRC, someone correct me if I am wrong!) and each time a dir is read from a different brick I bet the access time is different.
</pre>
<blockquote type="cite">
<pre wrap="">
For example:
# time rsync -av --inplace --whole-file --ignore-existing --delete-after
gromm/* /mnt/gromm/
building file list ... done
Maildir/ ## This part takes a long time.
Maildir/.INBOX.Trash/
Maildir/.INBOX.Trash/cur/
Maildir/.INBOX.Trash/cur/1429836077.H817602P21531.pop.lightspeed.ca:2,S
Maildir/.INBOX.Trash/tmp/ ## The previous three lines took nearly
no time at all.
Maildir/cur/ ## This takes a long time.
Maildir/cur/1430160436.H952679P13870.pop.lightspeed.ca:2,S
Maildir/new/
Maildir/tmp/ ## The previous lines again take no time
at all.
deleting Maildir/cur/1429836077.H817602P21531.pop.lightspeed.ca:2,S
## This delete did take a while.
sent 1327634 bytes received 75 bytes 59009.29 bytes/sec
total size is 624491648 speedup is 470.35
real 0m26.110s
user 0m0.140s
sys 0m1.596s
So, rsync reports that it wrote 1327634 bytes at 59 kBytes/sec, and the
whole operation took 26 seconds. To write 2 files that were around 20-30
kBytes each and delete 1.
The last rsync took around 56 minutes, when normally such an rsync would
have taken 5-10 minutes, writing over the network via ssh.
</pre>
</blockquote>
<pre wrap="">
It may have something to do with the access times not being in sync across replicated pairs. Maybe some has experience with this / could this be tripping up rsync?
-b
</pre>
<blockquote type="cite">
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</pre>
</blockquote>
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