linux

I found a machine which is not so ancient and did some tests with Xen on it.

Dear lazyweb, use the following code to clean out a filesystem namespace on linux:

mount ("root", "root", NULL, MS_BIND, NULL);
pivot_root ("root", "root/tmp");
chdir ("/");
umount2 ("/tmp", 2);
mount ("none", "/proc", "proc", 0, NULL);

Xen support finally landed in upstream Linux. Okay, it is rather limited yet, but usable.

It supports the following:

• Unprivileged domain (domU).
• x86_32 (i386 without PAE) and x86_32p (i386 with PAE).
• Console.
• netfront and blkfront.

Changes to the old Xen patch:

• Block devices does not support takeover of hdXY and sdXY. Use xvcX (xvca, xvcb, ...) as device names.
• Console is hvc0. You must supply console=hvc0 at the command line. (Use the extra definition in the Xen domain config file.)

Yet missing things:

• Suspend, resume (also makes migration impossible).
• Ballooning.
• x86_64. Xen upstream currently waits for an unified x86 tree.
• Privileged domain (dom0).
• netback, blkback, pciback and pcifront.

The linux kernel includes a SCSI target infrastructure since 2.6.20. Most of the code is located in the userspace and supports iSCSI, ibm i/pSeries virtual SCSI and Xen SCSIback.

To work properly it needs a bunch of patches on top of 2.6.21-rc.

After I got it working I did some tests with bonnie. First the target:

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
                 2G           32124  17 18063   6           45815   4 324.6   0

Now with the vSCSI initiator:

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
                 2G           18513   9 16208   5           34003   3 221.4   0

And the iSCSI initiator:

Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
                 2G           31631  14 12809   4           39241   5 306.3   1

As this tests was done on one OpenPower machine, all transfers uses DMA between the two systems.

The vscsi case is currently limited to 128KiB per request, maybe this is a problem.

It happened again. The linux-2.6 2.6.20-1 release failed for arches which we don't build snapshots for. This means that none of them was ever built in the time after I commited the whole stuff.

As this happens over and over again I consider this a real problem now. So the following arches needs new debian-kernel maintainers: alpha, hppa, and mips.

Nein, man sollte sich nicht wundern, dass das System sich so träge anfühlt, wenn /proc/mdstat folgendes zeigt:

md0 : active raid5 sdb[0] sdd[2] sdc[1]
      67108608 blocks level 5, 128k chunk, algorithm 2 [3/3] [UUU]
      [==========>..........]  resync = 53.2% (17870972/33554304) finish=7.3min speed=35319K/sec