我在 Ubuntu 12.04 伺服器上使用 SSD 儲存大約 460GB 的資料。 （驅動器可容納 560GB，因此大約已滿 88%。）我有一個程序，可以對數據進行大量隨機訪問（不寫入），我上次（正常）運行該程序是在幾天前。昨天運行的時候，突然比以前慢了許多。該程式只是隨機存取驅動器。
以前我每秒可以進行大約 5000 次隨機查找；現在我只得到大約 100。 （我去年對一些問題進行了基準測試。）
我最近做的唯一一件事就是安裝 gcc 4.7 並升級我的所有軟體包。但是，我嘗試用 clang 編譯所有內容，但沒有發現任何差異。
驅動器格式化為ext4唯一的選項errors=remount-ro。我嘗試重新啟動機器並修剪設備，但它沒有改變任何事情。對程式碼進行分析表明，它所有的時間都花在open,close和mmap調用上。 （請注意，我沒有直接呼叫 mmap —— 我使用的是 allC樣式fopen fseek和fread呼叫。）
知道什麼可能導致這種情況嗎？如果有可能的話，我可以重新格式化磁碟機。
編輯：這是 2TB HDD 和 500GB SSD 的一些基準數據
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
這是以下的輸出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.
[編輯：我正在後台繼續研究這個問題。當我解決這個問題時，我會在這裡發布一些內容。
答案1
所以，最終的答案有點尷尬，因為我應該可以弄清楚，但我找錯地方了。關鍵的線索在於硬碟速度的問題——測試顯示它也變慢了。
我處理讀取磁碟上資料的類別的內部緩衝區有一個預設的讀取大小。進行隨機存取時，該值應該相對較小，因為稍後您不會使用任何緩衝資料。當順序對整個檔案執行操作時，較大的值可提供更好的效能，因為您將重複使用資料。鑑於這是一段共享程式碼中的常數，使用該程式碼對一個應用程式進行調整基本上破壞了隨機存取的調整，從而導致我遇到的速度大幅下降。