四弦:
空弦由粗至細為E、A、D、G電子貝斯已經不僅只有基本的4弦，也有5弦和6弦之別，而5弦的電子貝斯，從第一弦到第五弦（由細到粗）的空弦音分別為：G、D、A、E、B，也有的空弦音分別為：C、G、D、A、E，依各大廠商自訂；至於6弦的電子貝斯，從第一弦到第六弦的空弦音分別為：C、G、D、A、E、B
2013年4月20日 星期六
Bass低音吉他基本知識
https://zh.wikipedia.org/wiki/%E9%9B%BB%E8%B2%9D%E6%96%AF
電子貝斯已經不僅只有基本的4弦，也有5弦和6弦之別，而5弦的電子貝斯，從第一弦到第五弦（由細到粗）的空弦音分別為：G、D、A、E、B，也有的空弦音分別為：C、G、D、A、E，依各大廠商自訂；至於6弦的電子貝斯，從第一弦到第六弦的空弦音分別為：C、G、D、A、E、B
電子貝斯已經不僅只有基本的4弦，也有5弦和6弦之別，而5弦的電子貝斯，從第一弦到第五弦（由細到粗）的空弦音分別為：G、D、A、E、B，也有的空弦音分別為：C、G、D、A、E，依各大廠商自訂；至於6弦的電子貝斯，從第一弦到第六弦的空弦音分別為：C、G、D、A、E、B
Python為"強型別"的語言
在Python中，字串是不可變動的（Immutable），所以+實際會產生新的字串，在強弱型別的光譜中，Python比較偏強型別，型態較不能自行轉換，例如Python中，不能混合字串與數字進行+運算，你得自己將數字轉為字串，才可以進行字串串接：
| >>> 'score: ' + 90Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: Can't convert 'int' object to str implicitly >>> 'score: ' + str(90)'score: 90' >>> |
python在函式參數傳遞上的重要基礎概念: *args 與 **kwargs 到底有啥不一樣呢?
好！！為啥會談論到這個東西？！因為python跟一般所學的C/C++很不一樣
一般來說 在呼叫函式的時候 是以 argument = parameter 的方式傳入
(引數) (參數)
而python在引數(arguments)這一塊有所謂的匹配模式(match pattern)概念在。
Q: 至於Python有那些的匹配模式呢!?
ANS：
一般來說可以分成兩種狀況：
以”位置”的方式來匹配
----由左到右的方式進行匹配
以”關鍵字”的方式來匹配
---- 以引數的名稱來進行匹配
而引數在設定有兩種額外的方法：
1. 引數預設值
在python的函式中可以指定引數的預設值。(以name=value的型式)
ex: func( x=3, y=2, z=1)
2. 變動引數(varargs)
-- python中，在函式宣告時可以利用萬用字元(*)來收集任意數量的額外引數(此概念是源自於C語言的varargs) ;
-- 而函式在呼叫時，可以用萬用字元(*)將引數集合體給分解成個別的引數，表示欲傳遞任意多個引數。
[Function定義語法格式]
def function_name(param1=arg1, param2=arg2, ....):
"""
Here is function body !!!
"""
[引數的匹配方式]
呼叫
語法 位置 說明
func(value) 呼叫者 普通引數: 以"位置"來匹配。
func(name=value) 呼叫者 關鍵字引數:以"名稱"來匹配。
func(*name) 呼叫者 把name之中所有物件傳遞進來，當作個別的位置引數。
func(**name) 呼叫者 把name之中的所有key/value pairs傳遞進來，當成個別關鍵字引數。
*/**在呼叫時，是解開任意數量之引數
定義
def func(name) 函式 普通引數: 以"位置"或"名稱"的方式去匹配
def func(name=value) 函式 預設引數值(如果在沒呼叫時傳遞)
def func(*name) 函式 先匹配再收集剩餘的"位置引數"在tuple中
def func(**name) 函式 先匹配再收集剩餘的"關鍵字引數"在dict(辭典)中
*/**在定義時，是建立任意數量之引數
Reference:
http://www.loliman3000.com/tech/2fe2eea4a80e94fd3811629.php
Associative Arrays in Bash Scripts
http://stackoverflow.com/questions/688849/associative-arrays-in-shell-scripts
http://www.artificialworlds.net/blog/2012/10/17/bash-associative-array-examples/
http://www.gnu.org/software/bash/manual/html_node/Arrays.html
http://stackoverflow.com/questions/6660010/bash-how-to-assign-an-associative-array-to-another-variable-name-e-g-rename-t
http://www.artificialworlds.net/blog/2012/10/17/bash-associative-array-examples/
http://www.gnu.org/software/bash/manual/html_node/Arrays.html
http://stackoverflow.com/questions/6660010/bash-how-to-assign-an-associative-array-to-another-variable-name-e-g-rename-t
SFP: Small Form Pluggable
GBIC
SFP
SFP是SMALL FORM PLUGGABLE的縮寫，可以簡單的理解為GBIC的升級版本。SFP模組體積比GBIC模組減少一半，可以在相同的面板上配置多出一倍以上的埠數量。SFP模組的其他功能基本和GBIC一致。有些交換機廠商稱SFP模組為小型化GBIC（MINI-GBIC）。 SFP模組體積比GBIC模組減少一半,可以在相同的面板上配置多出一倍以上的埠數量。SFP模組的其他功能基本和GBIC相同。詳全文 什麼是GBIC？什麼是SFP？光纖分為哪幾種？-Optech Technology 歐普科技-新浪部落 http://blog.sina.com.tw/optech/article.php?pbgid=70553&entryid=586142
光纖: 單模光纖 vs 多模光纖
單模光纖
多模光纖
Reference:
http://blog.sina.com.tw/optech/article.php?pbgid=70553&entryid=586142
cinder-manage
Usage:
cinder-manage sm flavor_create <label> <description>
cinder-manage sm flavor_delete<label>
cinder-manage sm backend_add <flavor label> <SR type> [config connection parameters]
Note: SR type and config connection parameters are in keeping with the Xen Command Line Interface.http://support.citrix.com/article/CTX124887
cinder-manage sm backend_delete <backend-id>
Examples:
cinder-manage sm flavor_create gold “Not all that glitters”
cinder-manage sm flavor_delete gold
cinder-manage sm backend_add gold nfs name_label=toybox-renuka server=myserver serverpath=/local/scratch/myname
cinder-manage sm backend_remove 1
XCP / Citrix Xenserver Volume Drivers on OpenStack
PS: Cinder是由Folsom版本開始從原本的nova-volume這部分去進行抽離的子專案
XenAPINFS is a Block Storage (Cinder) driver which is using an NFS share through XenAPI's Storage Manager to store virtual disk images and exposing those virtual disks as volumes.
XenAPINFS不能直接存取NFS，只能透過XenAPI Storage Manager來存取NFS。
( This driver is not accessing the NFS share directly, it is only accessing the share through XenAPI Storage Manager. )
This driver should be considered as a reference implementation for using XenAPI's storage manager in OpenStack ( present in XenServer and XCP).
Source Code:
nova,
https://github.com/openstack/nova/blob/stable/folsom/nova/volume/xensm.py
cinder,
https://github.com/openstack/cinder/blob/stable/folsom/cinder/volume/xensm.py
XenAPINFS
XenAPINFS is a Block Storage (Cinder) driver which is using an NFS share through XenAPI's Storage Manager to store virtual disk images and exposing those virtual disks as volumes.XenAPINFS不能直接存取NFS，只能透過XenAPI Storage Manager來存取NFS。
( This driver is not accessing the NFS share directly, it is only accessing the share through XenAPI Storage Manager. )
This driver should be considered as a reference implementation for using XenAPI's storage manager in OpenStack ( present in XenServer and XCP).
配置方式
- Local:
推薦的做法，這樣的話可以使用qemu-img，但必須在當作Storage Controller上的XCP/Xenserver host上開啟一台PV guest VM安裝 cinder + XenAPINFS driver - Remote:
不需要使用PV guest VM，直接拿XCP/Xenserver當作Storage Controller。但這樣的話只能用VDI格式的VHD。
Source Code:
1. Grizzly cinder, https://github.com/openstack/cinder/blob/stable/grizzly/cinder/volume/drivers/xenapi/sm.pyXenAPI Storage Manager Volume Driver ( only in Folsom version, 在grizzly版中似乎已經移除 )
The Xen Storage Manager Volume driver (xensm) is a XenAPI hypervisor specific volume driver
Source Code:
nova,
https://github.com/openstack/nova/blob/stable/folsom/nova/volume/xensm.py
cinder,
https://github.com/openstack/cinder/blob/stable/folsom/cinder/volume/xensm.py
功用:
- provide basic storage functionality, including volume creation and destruction, on a number of different storage back-ends.
- It also enables the capability of using more sophisticated storage back-ends for operations like cloning/snapshots, etc.
The list below shows some of the storage plugins already supported in Citrix XenServer and Xen Cloud Platform (XCP):
- NFS VHD:Storage repository (SR) plugin which stores disks as Virtual Hard Disk (VHD) files on a remote Network File System (NFS).
- Local VHD on LVM:SR plugin which represents disks as VHD disks on Logical Volumes (LVM) within a locally-attached Volume Group.
- HBA LUN-per-VDI driver:SR plugin which represents Logical Units (LUs) as Virtual Disk Images (VDIs) sourced by host bus adapters (HBAs). E.g. hardware-based iSCSI or FC support.
- NetApp:SR driver for mapping of LUNs to VDIs on a NETAPP server, providing use of fast snapshot and clone features on the filer.
- LVHD over FC:SR plugin which represents disks as VHDs on Logical Volumes within a Volume Group created on an HBA LUN. E.g. hardware-based iSCSI or FC support.
- iSCSI:Base ISCSI SR driver, provides a LUN-per-VDI. Does not support creation of VDIs but accesses existing LUNs on a target.
- LVHD over iSCSI:SR plugin which represents disks as Logical Volumes within a Volume Group created on an iSCSI LUN.
- EqualLogic:SR driver for mapping of LUNs to VDIs on a EQUALLOGIC array group, providing use of fast snapshot and clone features on the array.
2013年4月19日 星期五
Kafka和Storm
Kafka
Kafka 是一個用於截取與管理資料流（Data Stream）的即時框架（Real-Time Framework），也就是訊息發佈與訂閱的分散式管理系統。像 Twitter 和 Square 就是用 Kafka 來做日誌檔的管理，以便即時監控與處理事件的發生。
Storm
Storm 則是用於處理這些訊息資料流的框架，它與 Kafka 之間的關係，就像是 Hadoop 分散式系統與 MapReduce 之間的關係，也就是 Kafka 用來儲存訊息，Storm 則用來處理這些訊息，但是，Kafka 和 Storm 的速度即時多了。”Linux Security Hardening
sysctl: used to modify kernel parameters at runtime
sysctl is an interface that allows you to make changes to a running Linux kernel.
With /etc/sysctl.conf you can configure various Linux networking and system settings such as:
With /etc/sysctl.conf you can configure various Linux networking and system settings such as:
- Limit network-transmitted configuration for IPv4
- Limit network-transmitted configuration for IPv6
- Turn on execshield protection
- Prevent against the common 'syn flood attack'
- Turn on source IP address verification
- Prevents a cracker from using a spoofing attack against the IP address of the server.
- Logs several types of suspicious packets, such as spoofed packets, source-routed packets, and redirects.
http://www.cyberciti.biz/faq/linux-kernel-etcsysctl-conf-security-hardening/
訂閱：
文章 (Atom)