<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<div class="moz-cite-prefix">On 14/02/13 15:26, Tony wrote:<br>
</div>
<blockquote
cite="mid:1360815963.39788.YahooMailNeo@web164503.mail.gq1.yahoo.com"
type="cite">
<div style="color:#000; background-color:#fff; font-family:times
new roman, new york, times, serif;font-size:12pt">
<div><span>Check the RAID card then, a lot of the ones doing
hardware RAID-1 don't write any extra meta-data to the disk
or mess the disk stucture up, they just write the data to
both disks at the same time. This means that you wouldn't
have any concerns about what happens if your RAID card fails
as either disk can be put into any machine and used as just
a normal disk. I haven't played with server hardware for
ages, but the entry-level IBM RAID using LSI Logic
controllers was like this, two disks, plain mirroring of the
disks to each other. Have to be very careful when replacing
a disk which one you mirror from/to as the controller
doesn't know because there is nothing "special" about the
disk that it can identify the "RAID structure" on the disk.<br>
</span></div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;">Whilst we're tlaking about
SSD & SAS/SATA, you can also get RAID controllers that
have the option to add SSD as cache disks to store frequently
used data on to give some of the benefit of fast access to SSD
without worrying about them dropping dead quite so much.<br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;">Most hardware RAID
controllers have a number of features to avoid the issue of
having to find the same identical model controller if one
dies, but this is a concern. There are several ways to work
around this, you can purchase HW maintenance from your vendor
and rely on them to have spares for you. If you think RAID
controller is a single vulnerability that you don't like, you
could purchase two and have a hot spare sitting on your shelf.
You could also build in some redundancy at higher layers so
that VM's are spread across multiple real machines and recover
without downtime if one fails, but you're talking bigger $$
there. Then there is the option of using something like DRDB
to give you a RAID-1 set across two machines which is quite
interesting:<br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><a class="moz-txt-link-freetext" href="http://www.drbd.org/">http://www.drbd.org/</a><br>
<span></span></div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;"><br>
</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;">regards,</div>
<div style="color: rgb(0, 0, 0); font-size: 16px; font-family:
times new roman,new york,times,serif; background-color:
transparent; font-style: normal;">Tony.</div>
<br>
</div>
</blockquote>
<snip><br>
<br>
Thats actually the setup I use<br>
A pair of Dell R210II's for the VM hosts, 24gb ram (buy it from 3rd
party vendors its still over priced but 1/4 the $2000 dell wants for
it)<br>
short computers too, fit in (big) wall mount cabinets.<br>
quad core xeon CPU<br>
<br>
bonded gig-E for data network<br>
point to point infiniband connection for cluster communications (it
was < $100 for the whole setup off ebay for a 10gbps link totally
worth it for the giggles if nothing else)<br>
<br>
pair of 1TB 7200RPM disks<br>
100GB raid1 (mdadm) for /<br>
the other 900 for VM space<br>
I have it set as 2 volume groups one per physical hdd, so mail
server on one, file server on the other, all the other things spread
around evenly. <br>
<br>
I use ganeti with KVM for managing the VM's<br>
It handles everything, it sets up DRBD mirroring to the other host
and I rely on that for "raid".<br>
Does live migration for you all the big boy toys in an open source
package, used by google.<br>
</body>
</html>