I am a Linux System Administrator , Who started my carrier in Jan 2014. I am writing this blog with issues,requirements etc things of a Linux System Administrator.
I hope it will help you and Please contact me if you want to write.
Today I am writing about how to create Software RAID. Creating Software RAID is pretty easy. All we need either 3 equal size partitions on different harddisks or 3 equal size harddisks.
In my approach , I am doing this in VmWare by choosing 3 virtual harddisks with equal 1 GB Size. Our first step is we need to make those harddisks as ready for RAID.
In your terminal type as
# fdisk -l
To see available partitions and then try to create RAID partitions in that.
If We assume my 3 harddisks as /dev/sdb,/dev/sdc,/dev/sdd then in your terminal
# fdisk /dev/sdb Then
[root@ns1 sysadmin]# fdisk /dev/sdb
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to switch off the mode (command 'c') and change display units to sectors (command 'u'). Command (m for help): m Command action a toggle a bootable flag b edit bsd disklabel c toggle the dos compatibility flag d delete a partition l list known partition types m print this menu n add a new partition o create a new empty DOS partition table p print the partition table q quit without saving changes s create a new empty Sun disklabel t change a partition's system id u change display/entry units v verify the partition table w write table to disk and exit x extra functionality (experts only) Command (m for help): n
I am selecting new partition here as primary with default size ,( all my 3 VHDS having same size)
Command action e extended p primary partition (1-4) p Partition number (1-4): 1 First cylinder (1-130, default 1): Using default value 1 Last cylinder, +cylinders or +size{K,M,G} (1-130, default 130): Using default value 130
Now we have to change Partition type to RAID , so
Command (m for help): t Selected partition 1 Hex code (type L to list codes): fd ( fd for auto RAID)
Now just verify
Command (m for help): p Disk /dev/sdb: 1073 MB, 1073741824 bytes 255 heads, 63 sectors/track, 130 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x8a6b2eca Device Boot Start End Blocks Id System /dev/sdb1 1 130 1044193+ fd Linux raid autodetect
All good , we can commit our changes.
Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. Syncing disks.
Same as above do the same for /dev/sdc and /dev/sdd and then finally it will be like
[root@ns1 sysadmin]# fdisk -l Disk /dev/sda: 21.5 GB, 21474836480 bytes 255 heads, 63 sectors/track, 2610 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00092c9c Device Boot Start End Blocks Id System /dev/sda1 * 1 64 512000 83 Linux Partition 1 does not end on cylinder boundary. /dev/sda2 64 2611 20458496 8e Linux LVM Disk /dev/sdb: 1073 MB, 1073741824 bytes 255 heads, 63 sectors/track, 130 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x8a6b2eca Device Boot Start End Blocks Id System /dev/sdb1 1 130 1044193+ fd Linux raid autodetect Disk /dev/sdc: 1073 MB, 1073741824 bytes 255 heads, 63 sectors/track, 130 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x6429c3f4 Device Boot Start End Blocks Id System /dev/sdc1 1 130 1044193+ fd Linux raid autodetect Disk /dev/sdd: 1073 MB, 1073741824 bytes 255 heads, 63 sectors/track, 130 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xe883f58a Device Boot Start End Blocks Id System /dev/sdd1 1 130 1044193+ fd Linux raid autodetect Disk /dev/mapper/VolGroup-lv_root: 18.9 GB, 18865979392 bytes 255 heads, 63 sectors/track, 2293 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000
Now we have to create RAID, Here I am choosing RAID 5 which needs minimum 3 RAID Harddisks
[root@ns1 sysadmin]# mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sdb1 /dev/sdc1 /dev/sdd1 mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md0 started.
RAID 5 Created. --level indicates RAID level and after number and name of the devices.
To see your RAID Information execute this command
[root@ns1 sysadmin]# mdadm --detail /dev/md0 /dev/md0: Version : 1.2 Creation Time : Tue Nov 11 00:05:20 2014 Raid Level : raid5 Array Size : 2086912 (2038.34 MiB 2137.00 MB) Used Dev Size : 1043456 (1019.17 MiB 1068.50 MB) Raid Devices : 3 Total Devices : 3 Persistence : Superblock is persistent Update Time : Tue Nov 11 00:05:26 2014 State : clean Active Devices : 3 Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Layout : left-symmetric Chunk Size : 512K Name : ns1.example.com:0 (local to host ns1.example.com) UUID : af2998ef:acc6cb1e:feb832f1:7f9b2f1b Events : 18 Number Major Minor RaidDevice State 0 8 17 0 active sync /dev/sdb1 1 8 33 1 active sync /dev/sdc1 3 8 49 2 active sync /dev/sdd1
Then we have to save our RAID Configuration.
In CentOS configuration file : /etc/mdadm.conf
In Debain baed /etc/mdadm/mdadm.conf
So save the configuration with
[root@ns1 sysadmin]# mdadm --detail --scan ARRAY /dev/md0 metadata=1.2 name=ns1.example.com:0 UUID=af2998ef:acc6cb1e:feb832f1:7f9b2f1b [root@ns1 sysadmin]# mdadm --detail --scan > /etc/mdadm.conf [root@ns1 sysadmin]#
if you want to see stats of your RAID
[root@ns1 sysadmin]# cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] md0 : active raid5 sdd1[3] sdc1[1] sdb1[0] 2086912 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]
To set any RAID Disk as failed/faulty # mdadm --fail /dev/md0 /dev/sdb1
To Remove any Disk from RAID # mdamd --remove /dev/md0 /dev/sdb1
To add new disk # mdadm --add /dev/md0 /dev/sdb1
If harddisk/partition has taken from another RAID , to flush all data in it before using into a new RAID # mdadm --zero-superblock /dev/sda1
Stop a Running RAID # mdadm --stop /dev/md0
and to start # mdadm --run /dev/md0
Its supposed to run but with research i have done it wont run/start.
I am getting error like
###########
Starting httpd: [Wed Nov 19 01:17:25 2014] [warn] VirtualHost website1.com:80 overlaps with VirtualHost userinfo.com:80, the first has precedence, perhaps you need a NameVirtualHost directive
###########
Its because I am doing name based virtual hosting with one common IP, So we have to add that IP for name based virtualhosting with a line in /etc/httpd/conf/httpd.conf
Today I am writing about how to rename MySQL Database.
So If you want to rename a database in MySQL dont forget taking backup of your Views,Procedures and Functions of current database. Because while you renaming changes wont apply for Views,Procedures and functions.
After you have taken the backup , We can go for renaming with the command below.
RENAME TABLE old_db.table TO new_db.table;
Here old_db is your old database name and new_db is your new database name. You have to execute this command for each table. And this is the way.
But what if we have a big database with 1000 tables ? executing the same above command for 1000 times is a stupid idea.
If you are using Linux you can use following BASH script to do that for you
for table in $(mysql -p -s -N -e "show tables from db1"); do mysql -s -N -e "rename table db1.$table to db2.$table"; done;
db1 is your old database name and db2 is your new database name and remaining everything will tool care by script only except giving password.:P
After executing the command successfully without any errors , you must have to restore that backup of Views,Proc's and Functions.
Errors: I have got one error with triggering. Generally some tables have triggers. So you copy the code of triggers and then delete those triggers. Then try to rename the table again.
After it got successful , just recreate the triggers for the same tables in new database.
I have done this trigger creation in MYSQL Workbench.
If you want to backup only Functions and not data of database then you can use this command
--routines = for including routines ( views,functions,procedures)
--no-create-info = Do not write CREATE TABLE statements that re-create each dumped
table.
--no-data = Do not write any row information for the table. This is very useful
if you want to get a dump of only the structure for a table.
--no-create-db = This option suppresses the CREATE DATABASE /*!32312 IF NOT EXISTS*/
db_name statements that are otherwise included in the output if the
--databases or --all-databases option is given.
--skip-out = --opt
This option is shorthand; it is the same as specifying
--add-drop-table--add-locks--create-options--disable-keys--extended-insert--lock-tables--quick--set-charset. It should
give you a fast dump operation and produce a dump file that can be
reloaded into a MySQL server quickly. AsofMySQL4.1,--optisonbydefault,butcanbedisabledwith--skip-opt. To disable only
certain of the options enabled by --opt, use their --skip forms; for
example, --skip-add-drop-table or --skip-quick.
