Have many disks. More disk spindles brings more than capacity alone! (Same as in databases)

Speed

Disk platter transfer speed

If you think that disk has constant transfer speed, ZCAV has interesting graphs

Individial disks

Slow laptop 2.5" 5400 disk

dpavlin@llin:~$ sudo hdparm -i /dev/sda

/dev/sda:

 Model=FUJITSU MHV2080BH                       , FwRev=00840028, SerialNo=        NW05T6B29HM5
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=DualPortCache, BuffSize=8192kB, MaxMultSect=16, MultSect=?16?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=156301488
 IORDY=on/off, tPIO={min:240,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5 
 AdvancedPM=yes: mode=0x80 (128) WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-3,4,5,6,7

 * signifies the current active mode

dpavlin@llin:~$ sudo hdparm -tT /dev/sda
/dev/sda:
 Timing cached reads:   1566 MB in  2.00 seconds = 782.85 MB/sec
 Timing buffered disk reads:   66 MB in  3.03 seconds =  21.79 MB/sec

Interesting numbers are BuffSize (cache in disk) and MaxMultSect which we want to use for read-ahead param:

hdparm -m 16 -a 16 /dev/sda

This will decrease a bit speed of linerar buffer reads which hdparm uses, but we will pull from disk only blocks which are allready in cache, improving random read/write performance.

To find optimal readahead for your drive using hdparm access pattern you can use hdparm-readahead.pl which will try different combinations for you.

Faster (!) external 3.5 USB disk (no hdparm -i on USB), but just because it's another disk not loaded by system.

dpavlin@llin:~$ sudo hdparm -tT /dev/sdb

/dev/sdb:
 Timing cached reads:   1508 MB in  2.00 seconds = 753.72 MB/sec
 Timing buffered disk reads:   56 MB in  3.03 seconds =  18.48 MB/sec

Software RAID

Drive info:

dpavlin@brr:~$ sudo hdparm -i /dev/sdd

/dev/sdd:

 Model=WDC WD5000AAKS-00YGA0                   , FwRev=12.01C02, SerialNo=     WD-WCAS80929678
 Config={ HardSect NotMFM HdSw>15uSec SpinMotCtl Fixed DTR>5Mbs FmtGapReq }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=50
 BuffType=unknown, BuffSize=16384kB, MaxMultSect=16, MultSect=?16?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=976773168
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: Unspecified:  ATA/ATAPI-1,2,3,4,5,6,7

 * signifies the current active mode

Speed of individual drives in array:

dpavlin@brr:~$ sudo hdparm -tT /dev/sda /dev/sdb /dev/sdd

/dev/sda:
 Timing cached reads:   1982 MB in  2.00 seconds = 991.18 MB/sec
 Timing buffered disk reads:  232 MB in  3.03 seconds =  76.67 MB/sec

/dev/sdb:
 Timing cached reads:   2010 MB in  2.00 seconds = 1004.95 MB/sec
 Timing buffered disk reads:  228 MB in  3.01 seconds =  75.85 MB/sec

/dev/sdd:
 Timing cached reads:   2006 MB in  2.00 seconds = 1003.01 MB/sec
 Timing buffered disk reads:  230 MB in  3.01 seconds =  76.47 MB/sec

How are hey assembled into /dev/md0 RAID 5 array:

dpavlin@brr:~$ cat /proc/mdstat 
Personalities : [raid6] [raid5] [raid4] 
md0 : active raid5 sdd1[0] sda1[2] sdb1[1]
      976767872 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

Speed of array

dpavlin@brr:~$ sudo hdparm -tT /dev/md0

/dev/md0:
 Timing cached reads:   1986 MB in  2.00 seconds = 993.20 MB/sec
 Timing buffered disk reads:  434 MB in  3.01 seconds = 144.41 MB/sec

As expected RAID 5 speed is 75 + 75 + 0 (parity disk) ~ 144 MB/sec

Temperature

Disks don't like it hot!

root@brr:~# hddtemp /dev/sda /dev/sdb /dev/sdd
/dev/sda: WDC WD5000AAKS-00YGA0: 33°C
/dev/sdb: WDC WD5000AAKS-00YGA0: 32°C
/dev/sdd: WDC WD5000AAKS-00YGA0: 32°C

On output above, middle disk is /dev/sda so it's 1° hotter than other two. I could mitigate this with additional fan on front of case, but it's making enough noise already, so I'll leave it as is.

Data security

Smart

root@brr:~# smartctl --all /dev/sda | head -20
smartctl version 5.38 [i686-pc-linux-gnu] Copyright (C) 2002-8 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital Caviar Second Generation Serial ATA family
Device Model:     WDC WD5000AAKS-00YGA0
Serial Number:    WD-WCAS80815866
Firmware Version: 12.01C02
User Capacity:    500,107,862,016 bytes
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   8
ATA Standard is:  Exact ATA specification draft version not indicated
Local Time is:    Sat Oct 11 00:27:01 2008 CEST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

Before you start to beleve in SMART as solution to all disk health problems, read Failure Trends in a Large Disk Drive Population

See also Bad block HOWTO for smartmontools if you ever get smart errors and don't just want to throw out your disk.

RAID

Also interesting is Some RAID Issues

Read also Why RAID 5 stops working in 2009

http://kvm.qumranet.com/kvmwiki/FAQ

Install

sudo apt-get install kvm

Migration

http://kvm.qumranet.com/kvmwiki/Migration

• 01-kvm-start.sh - how to start kvm
• config - variables included in following scripts
• 02-kvm-migration-incomming.sh
• 03-kvm-migration-running.sh
• kvm-migration-demo.sh - wrap it all in demo

Prepare shared disk image

Usually, you will use nfs for this. Edit /etc/exports and add something like (if your local network is 192.168.1.x):

/rest           192.168.1.0/255.255.255.0(rw)

And start nfs server

dpavlin@llin:~$ sudo /etc/init.d/nfs-user-server start

New target

Mount shared storage and run qemu which will receive running machine

dpavlin@squeak:~$ mkdir mnt/rest
dpavlin@squeak:~$ sudo mount 192.168.1.13:/rest mnt/rest/
dpavlin@squeak:~$ ls -al mnt/rest/iso/gparted-live-0.3.9-4.iso 
-rw-r--r-- 1 dpavlin dpavlin 98347008 Oct  9 17:31 mnt/rest/iso/gparted-live-0.3.9-4.iso

dpavlin@squeak:~$ kvm -cdrom mnt/rest/iso/gparted-live-0.3.9-4.iso -incoming tcp://0:4444 -monitor stdio

Running source

dpavlin@llin:~$ kvm -m 128 -cdrom /rest/iso/gparted-live-0.3.9-4.iso -monitor stdio -no-kvm
QEMU 0.9.1 monitor - type 'help' for more information
(qemu) migrate tcp://192.168.1.30:4444

We use -no-kvm to disable kvm because our target machine doesn't have vmx|svm support!

Installation

sudo apt-get install qemu kqemu-source

kqemu module compilation on Debian:

sudo module-assistant a-i kqemu

OpenVZ is nice name-space virtualization, creating chroot jails on steroids, similar in spirit to Solaris zones. It ideal if you want to run single kernel and allocate resources using bean counters as opposed to hard-limits (20% of CPU as opposed to one core). Each slice is called VE.

Disk speed

dpavlin@zut:~$ sudo hdparm -tT /dev/cciss/c1d0 /dev/sda

/dev/cciss/c1d0:
 Timing cached reads:   2184 MB in  2.00 seconds = 1092.39 MB/sec
 Timing buffered disk reads:  324 MB in  3.02 seconds = 107.40 MB/sec

/dev/sda:
 Timing cached reads:   2144 MB in  2.00 seconds = 1071.89 MB/sec
 Timing buffered disk reads:  136 MB in  3.02 seconds =  45.02 MB/sec

Insert joke about enterprise storage

Add disk space to VE

We are using normal Linux LVM with single logical volume for all VEs.

First, resize logical volume:

root@koha-hw:~# vgextend -L +80G /dev/vg/vz
vgextend: invalid option -- L
  Error during parsing of command line.

root@koha-hw:~# lvextend -L +80G /dev/vg/vz
  Extending logical volume vz to 100.00 GB
  Logical volume vz successfully resized

root@koha-hw:~# resize2fs /dev/vg/vz 
resize2fs 1.40-WIP (14-Nov-2006)
Filesystem at /dev/vg/vz is mounted on /vz; on-line resizing required
old desc_blocks = 2, new_desc_blocks = 7
Performing an on-line resize of /dev/vg/vz to 26214400 (4k) blocks.
The filesystem on /dev/vg/vz is now 26214400 blocks long.

root@koha-hw:~# df -h /vz/
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg-vz      99G   20G   79G  21% /vz

Then, take a look how much space does VEs take:

root@koha-hw:~# vzlist -o veid,diskspace,diskspace.s,diskspace.h,diskinodes,diskinodes.s,diskspace.h
      VEID   DQBLOCKS DQBLOCKS.S DQBLOCKS.H   DQINODES DQINODES.S DQBLOCKS.H
    212052   11717220   15728640   20971520      61001     286527   20971520
    212226    6407804   10485760   12582912      69011     435472   12582912

alternativly, you can also execute df inside VEs:

root@koha-hw:~# vzlist -o veid -H | xargs -i sh -c "echo --{}-- ; vzctl exec {} df -h"
--212052--
Filesystem            Size  Used Avail Use% Mounted on
simfs                  15G   12G  3.9G  75% /
tmpfs                 2.0G     0  2.0G   0% /lib/init/rw
tmpfs                 2.0G     0  2.0G   0% /dev/shm
--212226--
Filesystem            Size  Used Avail Use% Mounted on
simfs                  10G  6.2G  3.9G  62% /
tmpfs                 2.0G     0  2.0G   0% /lib/init/rw
tmpfs                 2.0G     0  2.0G   0% /dev/shm

next, we will set diskpace on both VEs (becase we want them to share all available resources) to new logical volume size:

root@koha-hw:~# vzlist -o veid -H | xargs -i vzctl set {} --diskspace 100G:100G --save
Saved parameters for VE 212052
Saved parameters for VE 212226

This VEs are not in production, and one is development version of another. When we move to production, we want to enforce more strict limit on disk usage, to protect production machine from running out of disk space in case the development one goes wild.

VE management

We usually want to do some operations on bunch of VEs at once. This can be done using vzctl exec in one sweep like this:

Update Debian

vzlist -H -o veid | xargs -i vzctl exec {} 'apt-get update && apt-get -y upgrade' 2>&1 | tee ~/log

Quick reporting

You can read more about groupby.pl and sum.pl on my blog.

# install dependencies which are not part of standard lenny (sorry!)
cpanp i IPC::System::Simple

dpavlin@mjesec:~$ vzps -E axv --no-headers \
  | groupby.pl 'sum:($7+$8+$9*1024),1,count:1' --join 'sudo vzlist -H -o veid,hostname' --on 2 \
  | sort -rn | align | sum.pl -h
webgui.rot13.org  23      1026M OOOOOOOOOOOO                              1026M
0                385       855M OOOOOOOOOO------------                    1882M
saturn.ffzg.hr    32       544M OOOOOO-----------------------             2427M
eprints.ffzg.hr   18       351M OOOO-----------------------------         2778M
arh.rot13.org     20       224M OO----------------------------------      3003M

find getty processes

root@mljac:~# ps ax | grep getty | cut -c-5 | xargs vzpid
Pid     VEID    Name
5668    0       getty
5670    0       getty
5672    0       getty
5673    0       getty
5674    0       getty
5675    0       getty
9503    207016  getty
9504    207013  getty
9505    207013  getty
9534    207016  getty
9535    207015  getty
9536    207013  getty
9537    207013  getty
9538    207015  getty
9539    207015  getty
9540    207015  getty
9541    207016  getty
9542    207015  getty
9543    207016  getty
9545    207013  getty
9546    207013  getty
9547    207015  getty
9548    207016  getty

devices inside VE

For example, fuse

dpavlin@brr:/dev$ vzctl set 100 --devices c:10:229:rw --save

Links

• Recent Advances in the Linux Kernel resource management

vz-tools

sudo apt-get install libio-prompt-perl libregexp-common-perl libdata-dump-perl

sudo apt-get install host

svn co svn://svn.rot13.org/vz-tools/trunk vz-tools

cd vz-tools
perl Makefile.PL
make

./vz-create.pl

./vz-create.pl my-new-ve.exmple.com

./vz-create.pl 192.168.42.42

root@black:~/vz-tools# time ./vz-clone.pl create 1001
Clone VE 1001 -> 101001
found LV /dev/vg/vz for /vz
vzquota : (warning) Quota is running, so data reported from quota file may not reflect current values
quota for 1001 | 10485760 < 20971520 | usage: 7826792
using existing /dev/vg/vz-clone-101001
Mounting /dev/vg/vz-clone-101001 to /tmp/vz-clone-101001
rsync /vz/private/1001 -> /tmp/vz-clone-101001/private
101001 new IP number: 10.42.42.42
101001 new hostname: clone-42.example.com

Please review config file: /etc/vz/conf/101001.conf
Add NAT for new VE with: iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
Start clone of 1001 with: vzctl start 101001

real    1m57.347s
user    0m2.252s
sys     0m8.591s

Related posts on my blog