装配SSD

@2015-05-04

大约在半年之前把，台式机的HDD就被SMART检查出有问题了，但是考虑到更换系统挺麻烦的，就一直拖着。直到最近觉得不太能忍受了，开机需要60s以上，打开浏览器什么的都需要等一段时间，最不能忍受的是编辑文件保存一下就需要等1-2s. 然后看了一下自己硬盘空间，虽然是1TB但是实际只使用了<50G，所以买个250G的SSD应该是足够了。

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想到了就买，也没有在太多品牌和价格上纠结，就从 京东 上买了这款：三星（SAMSUNG）850 EVO系列 250G 2.5英寸 SATA-3固态硬盘(MZ-75E250B/CN). 安装好系统之后，继续挂着原来的HDD，这样可以把原来硬盘上的文件copy过来。从安装到配置好，大约花了2个小时左右，主要还是SSD的读写速度快。现在启动时间大约在10s以内，打开浏览器2-3s左右，感觉好极了。

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之前看过SSD的 科普文章 说TRIM指令可以让SSD利用率更高，所以最好确认自己的SSD支持TRIM指令。下面命令用来确认支持TRIM，grep "Data Set Management TRIM supported (limit 8 blocks)" 

➜  ~  sudo hdparm -I /dev/sda
[sudo] password for dirlt:

/dev/sda:

ATA device, with non-removable media
	Model Number:       Samsung SSD 850 EVO 250GB
	Serial Number:      S22SNXAG302833K
	Firmware Revision:  EMT01B6Q
	Transport:          Serial, ATA8-AST, SATA 1.0a, SATA II Extensions, SATA Rev 2.5, SATA Rev 2.6, SATA Rev 3.0
Standards:
	Used: unknown (minor revision code 0x0039)
	Supported: 9 8 7 6 5
	Likely used: 9
Configuration:
	Logical		max	current
	cylinders	16383	16383
	heads		16	16
	sectors/track	63	63
	--
	CHS current addressable sectors:   16514064
	LBA    user addressable sectors:  268435455
	LBA48  user addressable sectors:  488397168
	Logical  Sector size:                   512 bytes
	Physical Sector size:                   512 bytes
	Logical Sector-0 offset:                  0 bytes
	device size with M = 1024*1024:      238475 MBytes
	device size with M = 1000*1000:      250059 MBytes (250 GB)
	cache/buffer size  = unknown
	Nominal Media Rotation Rate: Solid State Device
Capabilities:
	LBA, IORDY(can be disabled)
	Queue depth: 32
	Standby timer values: spec'd by Standard, no device specific minimum
	R/W multiple sector transfer: Max = 1	Current = 1
	DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6
	     Cycle time: min=120ns recommended=120ns
	PIO: pio0 pio1 pio2 pio3 pio4
	     Cycle time: no flow control=120ns  IORDY flow control=120ns
Commands/features:
	Enabled	Supported:
	   *	SMART feature set
	    	Security Mode feature set
	   *	Power Management feature set
	   *	Write cache
	   *	Look-ahead
	   *	Host Protected Area feature set
	   *	WRITE_BUFFER command
	   *	READ_BUFFER command
	   *	NOP cmd
	   *	DOWNLOAD_MICROCODE
	    	SET_MAX security extension
	   *	48-bit Address feature set
	   *	Device Configuration Overlay feature set
	   *	Mandatory FLUSH_CACHE
	   *	FLUSH_CACHE_EXT
	   *	SMART error logging
	   *	SMART self-test
	   *	General Purpose Logging feature set
	   *	WRITE_{DMA|MULTIPLE}_FUA_EXT
	   *	64-bit World wide name
	    	Write-Read-Verify feature set
	   *	WRITE_UNCORRECTABLE_EXT command
	   *	{READ,WRITE}_DMA_EXT_GPL commands
	   *	Segmented DOWNLOAD_MICROCODE
	   *	Gen1 signaling speed (1.5Gb/s)
	   *	Gen2 signaling speed (3.0Gb/s)
	   *	Gen3 signaling speed (6.0Gb/s)
	   *	Native Command Queueing (NCQ)
	   *	Phy event counters
	   *	READ_LOG_DMA_EXT equivalent to READ_LOG_EXT
	    	DMA Setup Auto-Activate optimization
	    	Device-initiated interface power management
	   *	Asynchronous notification (eg. media change)
	   *	Software settings preservation
	    	Device Sleep (DEVSLP)
	   *	SMART Command Transport (SCT) feature set
	   *	SCT Write Same (AC2)
	   *	SCT Error Recovery Control (AC3)
	   *	SCT Features Control (AC4)
	   *	SCT Data Tables (AC5)
	   *	reserved 69[4]
	   *	DOWNLOAD MICROCODE DMA command
	   *	SET MAX SETPASSWORD/UNLOCK DMA commands
	   *	WRITE BUFFER DMA command
	   *	READ BUFFER DMA command
	   *	Data Set Management TRIM supported (limit 8 blocks)
Security:
	Master password revision code = 65534
		supported
	not	enabled
	not	locked
		frozen
	not	expired: security count
		supported: enhanced erase
	2min for SECURITY ERASE UNIT. 8min for ENHANCED SECURITY ERASE UNIT.
Logical Unit WWN Device Identifier: 5002538d4002292f
	NAA		: 5
	IEEE OUI	: 002538
	Unique ID	: d4002292f
Checksum: correct
Device Sleep:
	DEVSLP Exit Timeout (DETO): 50 ms (drive)
	Minimum DEVSLP Assertion Time (MDAT): 30 ms (drive)

为了利用好这块SSD，我还在网上查了一下推荐设置，总结如下：（一些意见我没有采纳）

高版本Linux内核已经支持自动对齐，但是似乎使用自带disk工具不能对新分区对齐。推荐使用GParted这个工具来做分区，它可以自动完成新分区的对齐。 

➜  ~  sudo fdisk -lu /dev/sda
[sudo] password for dirlt:

Disk /dev/sda: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00043176

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048   195311615    97654784   83  Linux
/dev/sda2       195313662   459102338   131894338+   f  W95 Ext'd (LBA)
/dev/sda5       195315712   390627327    97655808   83  Linux
/dev/sda6       400414720   459102207    29343744   83  Linux
/dev/sda7       390629376   400412671     4891648   82  Linux swap / Solaris

确保除了LBA之外的devices start都是2048的倍数 (start的单位是sector? 2048 * 512 bytes = 1MB)

另外关于SSD寿命问题可以看看这个帖子 http://zhidao.baidu.com/question/220559125.html

SSD完全不用担心寿命问题，SSD和机械硬盘的原理不一样，机械硬盘比如你系统装在C盘，C盘在磁盘的最外圈，所有它会一直在最外圈读和写。SSD的主控会让SSD平均写入，就是永远优先写在使用次数少的存储空间上，就是说就算你拿一个文件反复在SSD上复制删除，其实他每次写入的空间是不一样的，所以SSD的理论上更确切的应该说SSD可以写入容量X1万。拿主流64G的算，理论上就是60GX10000=60万G，实际应用算它打对折30万G。每天写入200G的话可以用4年多，但是能用200G吗？所有不用担心寿命问题，SSD的换掉肯定是被淘汰或坏掉的，绝对不会是写完的。SSD好坏很难说，基本用价格和品牌衡量吧，现在价格64G的在800以上的为好，再低就有问题了。因特尔，美光，海盗船，芝奇，金士顿什么的都可以。