Humble

What are Logical block size and Physical block size and How to find it ?

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In simple words, logical block size is the unit used by the  ‘kernel’ for read/write operations.. Physical block sizes are the ones which ‘disk controllers’ use for read/write operations.

Is there any way to display logical/ physical block sizes in your system?

Yep, there are:

1) Fetch this information from the ‘sysfs’:

‘sda’ is the example device

[root@humbles-lap ]# cat /sys/block/sda/queue/logical_block_size 512 [root@humbles-lap ]# cat /sys/block/sda/queue/physical_block_size 512 [root@humbles-lap ]#

2) Use ‘blockdev’ command to display the same information.

[root@humbles-lap ]# rpm -qf which blockdev util-linux-XXXX [root@humbles-lap ]#

–getss get logical block (sector) size –getpbsz get physical block (sector) size

[root@humbles-lap ]# blockdev –getss /dev/sda 512 [root@humbles-lap ]# blockdev –getpbsz /dev/sda 512 [root@humbles-lap ]#

Where are guest configuration files located in KVM

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I know it is a very simple question, but at the same time, if you don’t know the answer, it is not simple to you. That made me blog this information here.

In Fedora/RHEL, the guest configuration files are located under “/etc/libvirt/qemu” directory in the ‘name’ of the guest created in KVM.

[root@humbles-lap qemu]# pwd /etc/libvirt/qemu [root@humbles-lap qemu]#  ls networks rhel5.4-x86_64-kvm_backup.xml rhel5.4-x86_64-kvm.xml RHEL-5.xml rhevh.xml Window-2008.xml  [root@humbles-lap qemu]# cat rhel5.4-x86_64-kvm.xml |head -n 2 <domain type=’kvm’> <name>rhel5.4-x86_64-kvm</name> [root@humbles-lap qemu]#

Above output means, I have guests created in my system with names like rhevh, window-2008, rhel5.. etc

SR-IOV fails/error "SR-IOV: bus number out of range or ""not enough MMIO resources"

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I have seen SR-IOV ( Single Root I/O Virtulaization) fails with these error messages (“SR-IOV: bus number out of range or “not enough MMIO resources” ) when using SR-IOV capable hardware devices. Couple of things can contribute to this issue. One of them can be the subjected kernel calculate the size of a SR-IOV bar …

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Set scsi disk timeout value for guest virtio disks in qemu kvm…

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Today my friend asked me, how can he set “timeout” value for his KVM guest which uses virtio disks. ?. In guest, virtio devices will be represented as “vd{a,b,c..} devices.. He experienced to set that value for a scsi device (ex: echo 180 > /sys/block/sdd/device/timeout) .. My answer was, it is NOT required , so …

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virsh undefine delete guest configuration file in kvm

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Sometimes you may execute “virsh undefine” command .. but if you really didnt meant to delete the guest configuration from disk, please make sure you have a backup of the guest configuraiton file in a location which is NOT default for libvirt ie /etc/libvirt/qemu. Otherwise you may wonder where it went after virsh undefine command. …

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libvirt-guests

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The service called libvirt-guests are not familiar to most of the guys..This service has been provided by libvirt-client package. This service is on in 3,4,5 runlevels by default as you can see below : ### BEGIN INIT INFO # Provides: libvirt-guests # Required-Start: libvirtd # Required-Stop: libvirtd # Default-Start: 3 4 5 This is the …

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hdparm failed with error ” HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device. “

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One of my friend was trying to run ‘hdparm’ command against guest disk called ‘vdb’ and received above mentioned error. [root@lap]hdparm -t /dev/vdb **** HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device If the guest disk is shown as ‘vda,vdb..etc’ , those are virtio disks which run by virtio bus. ‘hdparm’ is a …

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How to know disk image format and other details of a guest disk using ‘qemu’ commands ?

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As you know there are different image formats which can be used for guest space.. Below are some of them with brief notes on it. > raw Raw disk image format (default). This format has the advantage of being simple and easily exportable to all other emulators. If your file system supports holes (for example …

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Network ports need to be opened in your firewall in context of RHEV

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Below services or operations happens on below mentioned ports.. So make sure that, those are opened..
54321                                : vdsm

22                                       : ssh

5634 – 6166                        : guest console access ports

49152 – 49216                   : VM migration port range

32023                                : Spice  usb redirection

 

It is already mentioned here .

http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Hypervisor_Deployment_Guide/chap-Deployment_Guide-Security_topics.html