Hello,<div><br></div><div>I am having performance problems with iSCSI and DRBD.</div><div><br></div><div>My setup is : </div><div><br></div><div>[client > write on xfs(no barrier) > LVM > iscsi initiator] > [iSCSI target on /dev/drbd0 > DRBD)] :</div>
<div><br></div><div>When DRBD disk is configured in default mode (with disk-flushes,md-flushes, disk-barrier), I have bad performance result.</div><div><br></div><div>Exemple :</div><div><br></div><div><div>>></div>
<div>root@vferon:/mnt# dd if=/dev/zero of=test count=10k bs=64k</div><div>10240+0 enregistrements lus</div><div>10240+0 enregistrements écrits</div><div>671088640 octets (671 MB) copiés, 25,9988 s, 25,8 MB/s</div><div><br>
</div><div>>></div><div>root@vferon:/mnt# dd if=/dev/zero of=test count=30k bs=64k</div><div>30720+0 enregistrements lus</div><div>30720+0 enregistrements écrits</div><div>2013265920 octets (2,0 GB) copiés, 129,431 s, 15,6 MB/s</div>
</div><div><br></div><div>---------------------------------------------------------------------------------------------------------</div><div>When DRBD disk is configured without barrier - </div><div><div><span class="Apple-tab-span" style="white-space:pre"> </span></div>
<div><span class="Apple-tab-span" style="white-space: pre; "> </span>disk {</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>no-disk-flushes;</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>no-md-flushes;</div>
<div><span class="Apple-tab-span" style="white-space:pre"> </span>no-disk-barrier;</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>}</div></div><div><br></div><div><div>>></div><div>root@vferon:/mnt# dd if=/dev/zero of=test count=10k bs=64k</div>
<div>10240+0 enregistrements lus</div><div>10240+0 enregistrements écrits</div><div>671088640 octets (671 MB) copiés, 11,8258 s, 56,7 MB/s</div><div>root@vferon:/mnt# </div><div><br></div><div>>></div><div>root@vferon:/mnt# dd if=/dev/zero of=test count=30k bs=64k</div>
<div>30720+0 enregistrements lus</div><div>30720+0 enregistrements écrits</div><div>2013265920 octets (2,0 GB) copiés, 41,1322 s, 48,9 MB/s</div></div><div><br></div><div>------------------------------------------------------------------------------------------------------------</div>
<div><br></div><div>So i found a way to improve performance, but it is not safe for my data.</div><div><br></div><div>I know about the barrier mechanism and I would like to know why it act like this with iSCSI and if any of you knows about the real cause of this if there is one.</div>
<div><br></div><div>I tried an other setup using NFSv4 instead of iSCSI and I don't have a such problem.</div><div><br></div><div>Thank you!</div><div><br></div><div>Feron Valentin</div>