by Teffin Varghese | Jul 20, 2018 | Android, Howtos, JavaScript, Linux, Mac, Networking, News, OS, Programming, Python, Review, Security, Servers, Windows
Blockchains are incredibly popular now a days.
What is a block chain how do they work what problems do they solve and how can they be used.
Like the name indicates a blockchain is a chain of blocks that contain information, this technique was originally described in 1991 by a group of researchers and was originally intended to time stamp digital documents so it’s not possible to backdate them or to tamper with them,almost like a notary.
However it went by mostly unused until it adapted by Satoshi Nakamoto in 2009 to created a digital crypto currency called bitcoin.
Now a blockchain is distributed ledger that is completely open to anyone they having interesting property, once a data has been recorded inside a blockchain it becomes very difficult to change it.
So how does that works!!!
Well take a closer look at a block. Each block contains some data, the hash of the block and the hash of the previous block.
The data that is stored inside the blocks defines the type of blockchain, the Bitcoin blockchain for example solves the details of the transactions such as the sender, the receiver and the amount of coins.
A block also has a hash, you can compare the hash to a fingerprint it identifies a block and all it’s contents and it is always unique just as a finger print.
Once the block is created it’s hash is being calculated. Changing something inside the block cause the hash to change, to another words hashes are very useful when you want to detect the changes to the block. If the fingerprint of the block changes it’s no longer the same block.
The third element inside of each block is the hash of the previous block and this effectively creates a chain of block and it’s the technique that makes the blockchain so secure.
Here we have a chain of three blocks and each block has an hash of the block and the hash of the previous block.
The block number three points to the block number two and the number two points to number one.
Now the first block is little bit special, it cannot points to it’s previous block, because it is the first block we call this block the Genesis block.
Now let’s say if we tamper with the second block, this causes the hash of the block to be changed as well, in turn that will make block 3 and all following blocks invalid, because they no longer store a valid hash of the previous block.
So changing a single block will make all following blocks invalid.
But using a hash is not enough to prevent tampering. Computers these days are faster and calculate hundred of thousands of hashes per second, you can effectively tamper with the block and recalculate all the hashes of other block to make the blockchain valid again.
Proof of Work
So to mitigate this blockchain has something called proof of work. it’s a mechanism that slows down the creation of a new block.
In bitcoins case it take about 10 minutes to calculate the required proof of work and add a new block to the chain, this mechanism makes it very hard to tamper with one block you need to recalculate the proof of work of all the following block.
So the security of the blockchain comes from creative use of hashing and the proof of work mechanism, but there is one more way that the block chain secured themselves and that is by being distributed. Instead of using a central entity to manage chains, blockchains use a peer to peer network and every one is allowed to join.
When someone joins this network he gets a full copy of the blockchain the node can use this to verify that everything is in order.
Now lets see what happens if some one creates a new block, that the block is sent to everyone on the network, each node then verify the blocks to make sure that the block is not tamper with and if everything checks out each node add the block to their own blockchain. All the nodes in this network creates consensus, the agree about what blocks are valid and which aren’t.
Blocks that are tampered with will be rejected by the other nodes in the network. So to successfully tamper with a blockchain, you need to tamper with all the blocks on the chain, redo the proof of work for each block and take control of more than 50% of the peer to peer network.
Only then when your tampered block becomes accepted by everyone else, so this is almost impossible to do.
Blockchains are also constantly evolving and one of the most recent development is the creation of smart contract.
The contracts are simple programs that are stored on the blockchain and it can be used to automatically exchange coins based on certain conditions.
The creation of blockchain technology peek the lot of peoples interest. Soon others realize that the technology can be used for other things likes
> Storing medical records.
>> Creating digital notary.
>> Collecting taxes.
So now you know what a blockchain is how it works on a basic level and what problems they solve.
by George Sruthin | Aug 18, 2017 | OS, Servers, Troubleshooting, Windows
I faced this error after changing the motherboard
so i googled as per the HPE advisory says its the issue is with the HBA card firmware so you need to use SPP to upgrade firmware, BTW the server is equiped with HBA240 please check the below given url for more reference to fix this issue you can use SPP as per HPE
but above step didnt fix my issue
So as suggested by HPE Tech team i have perform the steps given below
BIOS backup and Restore on replaced system board and check the status. Please find the process
1: Format a USB with FAT 32. and add a folder with a specific name so that you can confirm you have mounted to correct directory
2: Connect it directly with the Gen9 server.
3: Reboot the server.
4: While Posting Tap F9 while it prompts to enter into the UEFI BIOS.
5: Once in UEFI BIOS select " Embedded Application ".
6: Further Select " Embedded UEFI Shell ".
7: Once you are in " Shell > " prompt.
8: Type : map -r
9: It will list the connected USB as FS0: . this may vary. in my case i have seen BOTH "FS0: & FS1:" so you shoud check its your usb or other devices as i said earlier you should mount the device and check for the folder which we have created. type cd " FS0: " or " FS1 " OR " FSnth " number of devices and check .type " ls " this will show created folder, if your folder is missing change ID from FS0: TO FSnth: if folder is present we can continue to next step
n th = number of FS devices
10: Then type *FS0: ( Tap Enter )
11: It will change the directory into FS0 (ie: USB connected externally)
12: Then type " sysconfig -export filename.conf " from the FS0:\> prompt (This will export the BIOS configuration into a file named (filename .conf)
13: To edit the BIOS configuration file :
14: Type edit filename.conf from FS0:\> prompt
15: Once editing is done then tap Ctrl + Q at the same time to exit from the editing screen. If you want to save the changes then Tap " y " else " n ".
16: To import the changed file from the USB into the server type : sysconfig -import filename.conf from FS0:\> prompt
17: It will import the file and change the configuration in the server BIOS automatically.
18: To verify the changes reboot the server and check.
by Teffin Varghese | Aug 14, 2017 | Howtos, Linux, Networking, OS, Servers, Troubleshooting, VMware Esxi, Workstation
IPv6 [Internet Protocol version 6]
Introduction.
Internet Protocol Version 6 (IPv6) is a network layer protocol that enables data communications over a packet switched network.
Packet switching involves the sending and receiving of data in packets between two nodes in a network. The working standard for the IPv6 protocol was published by the Internet Engineering Task Force (IETF) in 1998.
The IETF specification for IPv6 is RFC 2460. IPv6 was intended to replace the widely used Internet Protocol Version 4 (IPv4) that is considered the backbone of the modern Internet.
IPv4 currently supports a maximum of approximately 4.3 billion unique IP addresses. IPv6 supports a theoretical maximum of 2128 addresses (340,282,366,920,938,463,463,374,607,431,768,211,456 to be exact!).
IPv6 and IPv4 share a similar architecture. The majority of transport layer protocols that function with IPv4 will also function with the IPv6 protocol. Most application layer protocols are expected to be interoperable with IPv6 as well, with the notable exception of File Transfer Protocol (FTP)
An IPv6 address consists of eight groups of four hexadecimal digits. If a group consists of four zeros, the notation can be shortened using a colon to replace the zeros.
A main advantage of IPv6 is increased address space. The 128-bit length of IPv6 addresses is a significant gain over the 32-bit length of IPv4 addresses, allowing for an almost limitless number of unique IP addresses.
IPv6 features
—————-
* Supports source and destination addresses that are 128 bits (16 bytes) long.
* Requires IPSec support.
* Uses Flow Label field to identify packet flow for QoS handling by router.
* Allows the host to send fragments packets but not routers.
* Doesn’t include a checksum in the header.
* Uses a link-local scope all-nodes multicast address.
* Does not require manual configuration or DHCP.
* Uses host address (AAAA) resource records in DNS to map host names to IPv6 addresses.
* Uses pointer (PTR) resource records in the IP6.ARPA DNS domain to map IPv6 addresses to host names.
* Supports a 1280-byte packet size (without fragmentation).
* Moves optional data to IPv6 extension headers.
* Uses Multicast Neighbor Solicitation messages to resolve IP addresses to link-layer addresses.
* Uses Multicast Listener Discovery (MLD) messages to manage membership in local subnet groups.
* Uses ICMPv6 Router Solicitation and Router Advertisement messages to determine the IP address of the best default gateway.
Adding a Temporary IPv6 Address on Linux.
=================================
Using “IP”
———-
/sbin/ip -6 addr add <ipv6address>/<prefixlength> dev <interface>
eg: /sbin/ip -6 addr add 2001:49f0:2920::a2/64 dev eth0
Using “ifconfig”
——————
/sbin/ifconfig <interface> inet6 add <ipv6address>/<prefixlength>
eg: /sbin/ifconfig eth0 inet6 add 2001:49f0:2920::a2/64
Add an IPv6 route through a gateway
============================
Using “ip”
———–
/sbin/ip -6 route add <ipv6network>/<prefixlength> via <ipv6address>
¬ [dev <device>]
eg: /sbin/ip -6 route add default via 2001:49f0:2920::1
Using “route”
—————
/sbin/route -A inet6 add <ipv6network>/<prefixlength> gw
¬ <ipv6address> [dev <device>]
eg: /sbin/route -A inet6 add default gw 2001:49f0:2920::1
Removing an IPv6 address
====================
Using “ip”
————
/sbin/ip -6 addr del <ipv6address>/<prefixlength> dev <interface>
eg: /sbin/ip -6 addr del 2001:49f0:2920::a2/64 dev eth0
Using “ifconfig”
——————
/sbin/ifconfig <interface> inet6 del <ipv6address>/<prefixlength>
eg: /sbin/ifconfig eth0 inet6 del 2001:49f0:2920::a2/64
by Teffin Varghese | Jun 10, 2017 | Howtos, Linux, Networking, OS, Servers, Storages, Troubleshooting
Distributed Replicated Block Device (DRBD)
DRBD is a distributed replicated storage system for the Linux platform. It is implemented as a kernel driver, several user space management applications, and some shell scripts. DRBD is traditionally used in high availability (HA) computer clusters, but beginning with DRBD version 9, it can also be used to create larger software defined storage pools with a focus on cloud integration.
Comparison to RAID-1
=====================
DRBD bears a superficial similarity to RAID-1 in that it involves a copy of data on two storage devices, such that if one fails, the data on the other can be used. However, it operates in a very different way from RAID and even network RAID.
In RAID, the redundancy exists in a layer transparent to the storage-using application. While there are two storage devices, there is only one instance of the application and the application is not aware of multiple copies. When the application reads, the RAID layer chooses the storage device to read. When a storage device fails, the RAID layer chooses to read the other, without the application instance knowing of the failure.
In contrast, with DRBD there are two instances of the application, and each can read only from one of the two storage devices. Should one storage device fail, the application instance tied to that device can no longer read the data. Consequently, in that case that application instance shuts down and the other application instance, tied to the surviving copy of the data, takes over.
Conversely, in RAID, if the single application instance fails, the information on the two storage devices is effectively unusable, but in DRBD, the other application instance can take over.
How it Works
============
The tool is built to imperceptibly facilitate communication between two servers by minimizing the amount of system resources used- It therefore does not affect system performance and stability.
DRBD facilitates communication by mirroring two separate servers- one server, although passive, is usually a direct copy of the other. Any data written to the primary server is simultaneously copied to the secondary one through a real time communication system. Any change made on the data is also immediately replicated by the passive server.
The passive server only becomes active when the primary one fails and collapses. When such a failure occurs, DRBD immediately recognizes the mishap and shifts to the secondary server. This shifting process however, is optional- it can either be manual or automatic. For users who prefer manual, one is required to authorize the system to shift to the passive server when the primary one fails. Automatic systems on the other hand, swiftly recognize problems within the primary servers and immediately shift to the secondary ones.
DRBD installation
=================
Install ELRepo repository on your both system:
———————————————-
# rpm -Uvh http://www.elrepo.org/elrepo-release-6-6.el6.elrepo.noarch.rpm
Update both repo
————————
yum update -y
setenforce 0
Install DRBD
—————–
[root@server1 ~]# yum -y install drbd83-utils kmod-drbd83
[root@server1 ~]# yum -y install drbd83-utils kmod-drbd83
Insert DRBD module manually on both machines or reboot
———————————————————————————
/sbin/modprobe drbd
Partition DRBD on both machines
———————————————-
[root@server1 ~]# fdisk -cu /dev/sdb
[root@server2 ~]# fdisk -cu /dev/sdb
Create the Distributed Replicated Block Device resource file
————————————————————————————-
[root@server1 ~]# vi /etc/drbd.d/clusterdb.res
resource clusterdb
{
startup {
wfc-timeout 30;
outdated-wfc-timeout 20;
degr-wfc-timeout 30;
}
net {
cram-hmac-alg sha1;
shared-secret sync_disk;
}
syncer {
rate 10M;
al-extents 257;
on-no-data-accessible io-error;
}
on server1 {
device /dev/drbd0;
disk /dev/sdb1;
address 192.165.1.111:7788;
flexible-meta-disk internal;
}
on server2 {
device /dev/drbd0;
disk /dev/sdb1;
address 192.165.1.111:7788;
meta-disk internal;
}
}
Make sure that DNS resolution is working
———————————————————-
/etc/hosts
192.168.1.110 server1 server1.example.com
192.168.1.111 server2 server2.example.com
Set NTP server and add it to crontab on both machines
—————————————————————————–
vi /etc/crontab
5 * * * * root ntpdate your.ntp.server
Copy DRBD configured and hosts file to server2
——————————————————————-
[root@server1 ~]# scp /etc/drbd.d/clusterdb.res server2:/etc/drbd.d/clusterdb.res
[root@server1 ~]# scp /etc/hosts server2:/etc/
Initialize the DRBD meta data storage on both machines
—————————————————————————–
[root@server1 ~]# drbdadm create-md clusterdb
[root@server2 ~]# drbdadm create-md clusterdb
Start the drdb on both servers
——————————————–
[root@server1 ~]# service drbd start
[root@server2 ~]# service drbd start
On the PRIMARY server run drbdadm command
——————————————————————
[root@server1 ~]# drbdadm — –overwrite-data-of-peer primary all
Check if Device disk initial synchronization to complete (100%) and check to confirm you are on primary server
———————————————————————————————————————————————————–
[root@server1 yum.repos.d]# cat /proc/drbd
version: 8.3.16 (api:88/proto:86-97)
GIT-hash: a798fa7e274428a357657fb52f0ecf40192c1985 build by phil@Build32R6, 2013-09-27 15:59:12
0: cs:SyncSource ro:Primary/Secondary ds:UpToDate/Inconsistent C r—–
ns:78848 nr:0 dw:0 dr:79520 al:0 bm:4 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:2017180
[>………………..] sync’ed: 27.0% (2037180/2096028)K
finish: 0:02:58 speed: 11,264 (11,264) K/sec
ns:1081628 nr:0 dw:33260 dr:1048752 al:14 bm:64 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0]
Create filesystem on Distributed Replicated Block Device device
——————————————————————————————-
[root@server1 yum.repos.d]# /sbin/mkfs.ext4 /dev/drbd0
mke2fs 1.41.12 (06-June-2017)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
131072 inodes, 524007 blocks
26200 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=536870912
16 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 26 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
Now you can mount DRBD device on your primary server
————————————————–
[root@server1 ~]# mkdir /data
[root@server1 ~]# mount /dev/drbd0 /data
You don’t need to mount the disk from secondary machines. All data you write on /data folder will be synced to machine2.
Adios 🙂
by Teffin Varghese | Jun 5, 2017 | Howtos, Linux, OS, Servers, Storages, Troubleshooting
Okay, What is RAID 🙂
RAID (Redundant Array of Independent Disks) is a data storage virtualization technology.
It combines multiple inexpensive,small disk drives into an array of disks in order to
provide redundancy, lower latency and maximized the chance to recover data from the hard drives
If they crashes. And there by improving the performance.
The RAID appears to the system as a single drive.
RAID can be implemented via Hardware devices as RAID controllers or via software
controlled by the Linux Kernel.
The most commonly used RAID levels are
RAID 0 [Minimum of 2 Disk]
RAID 1 [Minimum of 2 Disk]
RAID 5 [Minimum of 3 Disk]
RAID 10 [Minimum of 4 Disk]
==============================================
RAID 1
RAID 1 is also known as “disk
mirroring.” With RAID 1, data is copied seamlessly and simultaneously from one drive to another, creating an exact copy or mirror.
If one of the disk on raid array fails, the other can work without issues. It’s the simplest way to implement fault tolerance storage. But it slightly drag the performance.
This is useful when read performance or reliability is more important than the resulting data storage capacity.
The advantages of raid 1 are it offers excellent read speed and a write-speed that is comparable to that of a single drive and if a drive fails, data do not have to be rebuild, they just need to be copied to a new replacement drive.
The main disadvantage of RAID 1 is that the effective storage capacity is only half of the total drive capacity
because all data get written twice and software RAID 1 solutions do not always allow a hot swap of a failed drive.
Configuring RAID level 1 using mdadm.
Install mdadm on your server.
You can use the following commands to installmdadm.
For RHEL/CentOS/Fedora:
=======================
# yum install mdadm
And for Debian/Ubuntu:
=======================
#apt-get update
#apt-get install mdadm
The next step is to create a RAID array. For that create the disk partitions (with the same size) that are going to be the array members as RAID partition.
To create partitions you can use the following commands.
#fdisk -l | grep /dev/sd (This command will list the disks on the server.eg: the disks on the server are sdb & sdc)
Then choose one disk eg: sdb
#fdisk /dev/sdb
Then press ‘n’ for creating a new partition in /dev/sdb. Then press ‘p’ for use it as primary partition.
Enter the partition number. You can use the full size by just pressing two times ‘Enter key’.
Then press ‘t’ to choose the partition type. Then choose ‘fd‘ for Linux raid auto and press ‘Enter Key’ to apply it.
Pressing ‘p’ verify that the partition is created as Linux raid auto detect.
Press ‘w’ to save the changes.
Follow the same instructions to create new partition on /dev/sdc drive with the same partition size.
The next step is to create a RAID 1 sdb1,sdc1 array using command mdadm:
# mdadm –create –verbose –level=1 –raid-devices=2 /dev/md0 /dev/sdb1 /dev/sdc1
xxxxxxxxxx
–create–> create a new RAID device.
–verbose–>print information about its operations.
/dev/md0 is the new RAID device that we want to create.
–level–> defines the RAID level; in our case, RAID 1.
–raid-devices –> It specifies how many disks (devices) are going to be used in the creation of the new RAID device.(here 2 — /dev/sdb1 /dev/sdc1)
xxxxxxxxx
You can verify raid status using the following command.
#cat /proc/mdstat
#mdadm -E /dev/sd[b-c]1
# mdadm –detail /dev/md0
The next step is formatting the partition and creating a file system and mount the partition.
#mkfs.ext4 /dev/md0 –> to format the partition
To mount /dev/md0 to /raid1 perform the below steps.
# mkdir /raid1
# mount /dev/md0 /raid1
# df -H –> you can verify it is mounted or not.
To auto-mount RAID1 on system reboot, need to make an entry in ‘/etc/fstab‘ file.
For that add the following line to the fstab.
/dev/md0 /raid1 ext4 defaults 0 0
Then run ‘mount -a‘ to check whether there are any errors on fstab entry.
Now update /etc/mdadm/mdadm.conf or/etc/mdadm.conf file as follows:
ARRAY /dev/md0 devices=/dev/sdb1,/dev/sdc1 level=1num-devices=2 auto=yes
or
# mdadm –detail –scan >> /etc/mdadm.conf
That’s all for now. 🙂
by George Sruthin | Jan 27, 2016 | Howtos, Servers
When i was trying to add new 3TB hdd to HP DL 180 G6 Server which has a HP Smart Array P410 Controller in it , the HDD is only detecting as 800 GB HDD Check the error below
After getting this error i have noticed and read instructions which came with HDD , in that instructions it clearly Saying that if we need to add HDD Which has a Capacity of 2.2 TB or above we need to upgrade the Current Firmware to 5.0 or later and supported controllers as follows
- HP Smart Array P212 Controller
- HP Smart Array P410 Controller
- HP Smart Array P410i Controller
- HP Smart Array P411 Controller
- HP Smart Array P711m Controller
- HP Smart Array P712m Contorller
- HP Smart Array P812 Controller
Then i go to this Url to Download Latest Firmware for HP Smart Array P410 (also support for P212,P410i,P411,P711m,P712m,P812)
HP Smart Array P212, P410, P410i, P411, P711m, P712m, and P812 Controller Firmware Versions !
From this url you can download latest or older version of firmware !
after downloading and updating firmware you Must restart your server and check whether it detecting or not , for that you can select controller check the information tab in HP ACU or simply check driver version in Windows Device Manager !
once you find the firmware version is detected as 5.0 or above you can add your HDD & and once it detect as correct HDD space you can create Logical volume.
And also you need to do one importing thing ! once you add hdd and create logical volume in Smart Array Controller . you need to Create GPT volume in windows Disk Manager than MBR , because to use above 2 tb you need to use GPT instead of MBR !
Hope you find this post useful , please share like and comment 🙂
