我在 Ubuntu 12.04 服务器上使用 SSD 存储大约 460GB 的数据。（该驱动器可容纳 560GB，因此大约已占用 88%。）我有一个程序，它会对数据进行大量随机访问（不写入），我上次运行该程序（正常）是在几天前。当我昨天运行它时，它突然比以前慢了很多。该程序只是对驱动器进行随机访问。
以前我每秒可以进行大约 5000 次随机查找；现在我只能进行大约 100 次。这比对 HDD 进行随机访问要慢。（去年我对一些问题进行了基准测试。）
我最近唯一做的事情就是安装 gcc 4.7 并升级所有软件包。但是，我尝试使用 clang 编译所有内容，但没有发现任何差异。
驱动器的格式为，ext4唯一的选项是errors=remount-ro。我尝试重新启动机器并修剪设备，但并没有改变任何事情。分析代码显示它将所有时间都花在了open、close和mmap调用上。（请注意，我没有直接调用 mmap —— 我使用的是 all C-stylefopen fseek和fread调用。）
知道是什么原因造成的吗？如果有可能的话，我可以重新格式化驱动器。
编辑：以下是 2TB HDD 和 500GB SSD 的一些基准数据
sudo hdparm -Tt /dev/sdb1
/dev/sdb1:
Timing cached reads: 6814 MB in 2.00 seconds = 3410.05 MB/sec
Timing buffered disk reads: 458 MB in 3.00 seconds = 152.45 MB/sec
sudo hdparm -Tt /dev/sdc1
/dev/sdc1:
Timing cached reads: 6890 MB in 2.00 seconds = 3447.93 MB/sec
Timing buffered disk reads: 780 MB in 3.01 seconds = 259.36 MB/sec
以下是 的输出smartctl：
=== START OF INFORMATION SECTION ===
Model Family: Intel 320 Series SSDs
Device Model: INTEL SSDSA2CW600G3
Serial Number: CVPR140004B7600FGN
LU WWN Device Id: 5 001517 9596df196
Firmware Version: 4PC10362
User Capacity: 600,127,266,816 bytes [600 GB]
Sector Size: 512 bytes logical/physical
Device is: In smartctl database [for details use: -P show]
ATA Version is: 8
ATA Standard is: ATA-8-ACS revision 4
Local Time is: Sun Jan 26 16:46:53 2014 MST
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
General SMART Values:
Offline data collection status: (0x00) Offline data collection activity
was never started.
Auto Offline Data Collection: Disabled.
Self-test execution status: ( 0) The previous self-test routine completed
without error or no self-test has ever
been run.
Total time to complete Offline
data collection: ( 1) seconds.
Offline data collection
capabilities: (0x75) SMART execute Offline immediate.
No Auto Offline data collection support.
Abort Offline collection upon new
command.
No Offline surface scan supported.
Self-test supported.
Conveyance Self-test supported.
Selective Self-test supported.
SMART capabilities: (0x0003) Saves SMART data before entering
power-saving mode.
Supports SMART auto save timer.
Error logging capability: (0x01) Error logging supported.
General Purpose Logging supported.
Short self-test routine
recommended polling time: ( 1) minutes.
Extended self-test routine
recommended polling time: ( 1) minutes.
Conveyance self-test routine
recommended polling time: ( 1) minutes.
SCT capabilities: (0x003d) SCT Status supported.
SCT Error Recovery Control supported.
SCT Feature Control supported.
SCT Data Table supported.
SMART Attributes Data Structure revision number: 5
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE
3 Spin_Up_Time 0x0020 100 100 000 Old_age Offline - 0
4 Start_Stop_Count 0x0030 100 100 000 Old_age Offline - 0
5 Reallocated_Sector_Ct 0x0032 100 100 000 Old_age Always - 0
9 Power_On_Hours 0x0032 100 100 000 Old_age Always - 17833
12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 13
170 Reserve_Block_Count 0x0033 100 100 010 Pre-fail Always - 0
171 Program_Fail_Count 0x0032 100 100 000 Old_age Always - 0
172 Erase_Fail_Count 0x0032 100 100 000 Old_age Always - 0
183 Runtime_Bad_Block 0x0030 100 100 000 Old_age Offline - 0
184 End-to-End_Error 0x0032 100 100 090 Old_age Always - 0
187 Reported_Uncorrect 0x0032 100 100 000 Old_age Always - 0
192 Unsafe_Shutdown_Count 0x0032 100 100 000 Old_age Always - 5
199 UDMA_CRC_Error_Count 0x0030 100 100 000 Old_age Offline - 0
225 Host_Writes_32MiB 0x0032 100 100 000 Old_age Always - 3236658
226 Workld_Media_Wear_Indic 0x0032 100 100 000 Old_age Always - 4973
227 Workld_Host_Reads_Perc 0x0032 100 100 000 Old_age Always - 65
228 Workload_Minutes 0x0032 100 100 000 Old_age Always - 1067143
232 Available_Reservd_Space 0x0033 100 100 010 Pre-fail Always - 0
233 Media_Wearout_Indicator 0x0032 096 096 000 Old_age Always - 0
241 Host_Writes_32MiB 0x0032 100 100 000 Old_age Always - 3236658
242 Host_Reads_32MiB 0x0032 100 100 000 Old_age Always - 6437718
SMART Error Log Version: 1
No Errors Logged
SMART Self-test log structure revision number 1
No self-tests have been logged. [To run self-tests, use: smartctl -t]
Note: selective self-test log revision number (0) not 1 implies that no selective self-test has ever been run
SMART Selective self-test log data structure revision number 0
Note: revision number not 1 implies that no selective self-test has ever been run
SPAN MIN_LBA MAX_LBA CURRENT_TEST_STATUS
1 0 0 Not_testing
2 0 0 Not_testing
3 0 0 Not_testing
4 0 0 Not_testing
5 0 0 Not_testing
Selective self-test flags (0x0):
After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.
[编辑：我正在后台继续处理这个问题。当我解决这个问题后，我会在这里发布一些内容。]
答案1
所以，最终的答案有点令人尴尬，因为我本应该能够找到答案，但我找错了地方。关键线索在于硬盘速度的问题——测试表明硬盘速度也变慢了。
处理读取磁盘数据的类的内部缓冲区具有默认读取大小。进行随机访问时，该大小应该相对较小，因为您以后不会使用任何缓冲数据。当按顺序对整个文件执行操作时，较大的值可提供更好的性能，因为您将重复使用数据。鉴于这是一段共享代码中的常量，使用该代码对一个应用程序进行调整实际上会破坏对随机访问的调整，从而导致我所经历的严重减速。