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<div class="moz-cite-prefix">On 25/08/2013 15:06, Walter Robert
Ditzler wrote:<br>
</div>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"
lang="EN-US">to me here your question confuses a bit. About
what RAID you talk about? RAID0, RAID1 or RAID5? With RAID0
you have twice read performance in best case. But DRBD does
RAID1 over TCP/IP what means mirroring two disk/disk set. If
one fails the other one comes into operation.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"
lang="EN-US"><o:p> </o:p></span></p>
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</blockquote>
RAID1 gives you potentially twice the read performance of a single
disk, because the data is stored on two disks and both are available
for reads.<br>
<br>
So the question should have said: "if I have a DRBD mirrored pair,
can I configure it to do reads from both the primary and the
secondary?"<br>
<br>
I think the answer is probably "no", but I could be mistaken.
Running DRBD on top of two iSCSI volumes is a pretty unusual
configuration to say the least. In any case, access to the remote
copy would be slower than access to the local copy (since it would
involve going over the DRBD-DRBD link).<br>
<br>
With iSCSI you could simply attach the two iSCSI volumes onto the
same host, and use MD mirroring. No need for DRBD then (even if the
two iSCSI volumes are on different storage servers, you could attach
them both to the same host). And in this case you *would* have both
volumes available for reads.<br>
<blockquote cite="mid:007701cea19c$49f44b40$dddce1c0$@gmail.com"
type="cite">
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"
lang="EN-US">Next I don’t understand, when you got iSCSI
then you don’t need DRBD!</span></p>
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</blockquote>
Why not? iSCSI is about remote access to a block storage device.
DRBD is about data replication. They are two different things.<br>
<blockquote cite="mid:007701cea19c$49f44b40$dddce1c0$@gmail.com"
type="cite">
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US"
lang="EN-US"> In my mind iSCSI devices are all connected to
the same host</span></p>
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</blockquote>
Why? You can have multiple iSCSI targets on the same storage server,
or on different servers.<br>
<br>
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