<p class="MsoNormal">Hello,</p><p class="MsoNormal"><br></p><p class="MsoNormal">When you use a flavor with an ephemeral disk size different from zero, the instance is booted with an
extra virtual disk whose size is indicated by the ephemeral value (in GB).</p><p class="MsoNormal">Using cirros image, try a flavor with ephemeral disk size different from zero (you need to create one yourself because the "standard" flavors have ephemeral size equal to 0), then log into the just booted instance and type:</p>
<p class="MsoNormal"><br></p><p class="MsoNormal"></p><p class="MsoNormal">
</p><p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><b style><span style="font-size:9.0pt;line-height:115%;font-family:Courier">$ ls /dev/vd*</span></b></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">/dev/vda<span style> </span>/dev/vda1<span style>
</span>/dev/vdb</span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Disk /dev/vdb is a (virtual) disk, automatically created at
boot time, corresponding to the ephemeral disk space indicated by the flavor . Please note that /dev/vda, mounted as /dev/vda1, is the
boot disk, always created when you boot an instance.</p>
<p class="MsoNormal">Verify the size of the available disks; more specifically,
verify /dev/vdb:</p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><b style><span style="font-size:9.0pt;line-height:115%;font-family:Courier"><br></span></b></p><p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt">
<b style><span style="font-size:9.0pt;line-height:115%;font-family:Courier">$ sudo fdisk -l</span></b></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Disk /dev/vda:
1073 MB, 1073741824 bytes</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">255 heads, 63 sectors/track,
130 cylinders, total 2097152 sectors</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Units = sectors of
1 * 512 = 512 bytes</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Sector size
(logical/physical): 512 bytes / 512 bytes</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">I/O size
(minimum/optimal): 512 bytes / 512 bytes</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Disk identifier:
0x00000000</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier"> </span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier"><span style> </span>Device Boot<span style> </span>Start<span style> </span>End<span style> </span>Blocks<span style>
</span>Id<span style> </span>System</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">/dev/vda1<span style> </span>*<span style>
</span>16065<span style> </span>2088449<span style> </span>1036192+<span style>
</span>83<span style> </span>Linux</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier"> </span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Disk /dev/vdb:
1073 MB, 1073741824 bytes</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">16 heads, 63
sectors/track, 2080 cylinders, total 2097152 sectors</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Units = sectors of
1 * 512 = 512 bytes</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Sector size
(logical/physical): 512 bytes / 512 bytes</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">I/O size
(minimum/optimal): 512 bytes / 512 bytes</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Disk identifier:
0x00000000</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier"> </span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier">Disk /dev/vdb
doesn't contain a valid partition table</span></p>
<p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt"><span style="font-size:9.0pt;line-height:115%;font-family:Courier"> </span></p>
<p class="MsoNormal">Please note that /dev/vdb is made available as raw device,
meaning that you need to partition and format it before using.</p><p class="MsoNormal">You can find instructions on how to do that here <a href="http://docs.openstack.org/folsom/openstack-compute/admin/content/configure-nova-volume.html">http://docs.openstack.org/folsom/openstack-compute/admin/content/configure-nova-volume.html</a> (search for command fdisk)<br>
</p><p class="MsoNormal">Also note that this disk, being ephemeral, disappears when you terminate the VM. If you want to keep the data you produce with a VM that is destined to be terminated, you need to use Volumes that you explicitly create and attach using the services implemented by Cinder (former nova-volume).<br>
</p><p class="MsoNormal"><br></p>
<p></p><p class="MsoNormal">For what concerns the size you define for the boot disk, try and lunch two instances: one with flavor m1.tiny the other with m1.small:</p><p class="MsoNormal"><br></p><p class="MsoNormal">-- tiny --</p>
<p class="MsoNormal"><b>$ sudo fdisk -l<br></b><br>Disk /dev/vda: 41 MB, 41126400 bytes<br>255 heads, 63 sectors/track, 5 cylinders, total 80325 sectors<br>Units = sectors of 1 * 512 = 512 bytes<br>Sector size (logical/physical): 512 bytes / 512 bytes<br>
I/O size (minimum/optimal): 512 bytes / 512 bytes<br>Disk identifier: 0x00000000<br><br> Device Boot Start End Blocks Id System<br>/dev/vda1 * 16065 80324 32130 83 Linux<br><br>
</p><br><p class="MsoNormal">-- small --</p><p class="MsoNormal"><br></p><b>$ sudo fdisk -l<br></b><br>Disk /dev/vda: 21.5 GB, 21474836480 bytes<br>255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors<br>Units = sectors of 1 * 512 = 512 bytes<br>
Sector size (logical/physical): 512 bytes / 512 bytes<br>I/O size (minimum/optimal): 512 bytes / 512 bytes<br>Disk identifier: 0x00000000<br><br> Device Boot Start End Blocks Id System<br>/dev/vda1 * 16065 41929649 20956792+ 83 Linux<br>
<br><p class="MsoNormal"><br></p>
As you notice, the size indicated by the flavor has effects on the size of the boot disk.<br><br><br>Hope it helps,<br>Marco.<br><br><br><br>On Mon, Dec 3, 2012 at 7:03 PM, Ahmed Al-Mehdi <span dir="ltr"><<a href="mailto:ahmedalmehdi@gmail.com" target="_blank">ahmedalmehdi@gmail.com</a>></span> wrote:<br>
<div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello,<div><br></div><div>I instantiated a VM using the cirros image, using the pre-defined "m1.small" (1 VCPU, 2 GB Ram, 20G boot disk, 0 Ephemeral disk). I then logged into the console of the VM to view some system stats. The num of CPU and memory makes sense, but I am a bit confused on the storage aspect. I see the output of "df -h " as following:</div>
<div><br></div><div>$ df -h</div><div>Filesystem Size Used Available Use% Mounted on</div><div>/dev 1001.1M 0 1001.1M 0% /dev</div>
<div>/dev/vda1 23.2M 12.9M 9.1M 59% /</div><div>tmpfs 1004.1M 0 1004.1M 0% /dev/shm</div><div>tmpfs 200.0K 20.0K 180.0K 10% /run</div>
<div><br></div><div><br></div><div>What is the difference between Boot disk and Ephemeral disk?</div><div><br></div><div>How can I correlate the 20G boot disk to the output of "df -h".</div><div><br></div><div>
<br>
</div><div>Regards,</div><div>Ahmed.</div><div><br></div>
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