Wednesday, November 28, 2012

CloudBeat conversation with Paul Miller



wow it sure is strange seeing yourself on the telly...

Thursday, November 8, 2012

of disks and highly performing memories...


Assume you have enough host memory, and assume the following:

[root@parathyro-dom0]# mkdir /ram
[root@parathyro-dom0]# mount -t tmpfs -o size=50g,uid=107,gid=107,nr_inodes=10k,mode=0777 tmpfs /ram/

then assume you do something like this with it...

[root@parathyro-dom0]# time qemu-img create -f raw /ram/temp.raw 40G
Formatting '/ram/temp.raw', fmt=raw size=42949672960

real 0m0.002s
user 0m0.000s
sys 0m0.001s

Then a spot of this.
(You can't have cache="none" for this type of "drive"...)
[root@parathyro-dom0]# virsh edit parathyro-vm-clone

    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <source file='/ram/temp.raw'/>
      <target dev='vdb' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </disk>


You can see it does not take a great leap of imagination...


Tuesday, November 6, 2012

do not try to use unix LDAP queries against AD without this...

Ok short post this. If you have 1,000's of users and you are using this sort of foo to map your users to AD in linux:

[jcuff@atlas6203 home00]$ cat /etc/ldap.conf | grep posix
nss_map_objectclass posixAccount user
nss_map_objectclass posixGroup group

And your schema does not look like this (that little tick box has to be there):


Even with NSCD, you are going to be stuffed.

That is all.

I learned this the hardway today... amazing what you find when you are not a windows admin...

It is true, it is on the internet. We saw a 2x speed up on every getent related system operation as an added win.

postscript: HPC systems do a lot of getent... ;-)


[any opinions here are all mine, and have absolutely nothing to do with my employer]
(c) 2011 James Cuff