将服务器从centos 4升级到centos 6之后，系统只能使用12 Gb中的8个; 我以为有些错误，但事实并非如此（我试图与另一台服务器交换内存）我有6 x 2GB的DDR DIMM;
free total used free shared buffers cached Mem: 8195024 560508 7634516 0 37388 169116 -/+ buffers/cache: 354004 7841020 Swap: 4200956 0 4200956 和/ PROC / meminfo中
cat /proc/meminfo MemTotal: 8195024 kB MemFree: 7702732 kB Buffers: 29232 kB Cached: 106368 kB SwapCached: 0 kB Active: 93684 kB Inactive: 107164 kB Active(anon): 65476 kB Inactive(anon): 1032 kB Active(file): 28208 kB Inactive(file): 106132 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 4200956 kB SwapFree: 4200956 kB Dirty: 0 kB Writeback: 0 kB AnonPages: 65244 kB Mapped: 33532 kB Shmem: 1264 kB Slab: 211304 kB SReclaimable: 24852 kB SUnreclaim: 186452 kB KernelStack: 1960 kB PageTables: 11336 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 8298468 kB Committed_AS: 346860 kB VmallocTotal: 34359738367 kB VmallocUsed: 321300 kB VmallocChunk: 34359408376 kB HardwareCorrupted: 0 kB AnonHugePages: 8192 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 10176 kB DirectMap2M: 8378368 kB
这里有一些输出：
dmidecode -t 17 #dmidecode 2.10 SMBIOS 2.3 present. Handle 0x003A, DMI type 17, 27 bytes Memory Device Array Handle: 0x0039 Error Information Handle: Not Provided Total Width: 144 bits Data Width: 128 bits Size: 2048 MB Form Factor: DIMM Set: None Locator: A0 Bank Locator: Bank0/1 Type: DDR Type Detail: Synchronous Speed: 400 MHz Manufacturer: None Serial Number: None Asset Tag: None Part Number: None Handle 0x003B, DMI type 17, 27 bytes Memory Device Array Handle: 0x0039 Error Information Handle: Not Provided Total Width: 144 bits Data Width: 128 bits Size: 2048 MB Form Factor: DIMM Set: None Locator: A1 Bank Locator: Bank2/3 Type: DDR Type Detail: Synchronous Speed: 400 MHz Manufacturer: None Serial Number: None Asset Tag: None Part Number: None Handle 0x003C, DMI type 17, 27 bytes Memory Device Array Handle: 0x0039 Error Information Handle: Not Provided Total Width: 144 bits Data Width: 128 bits Size: 2048 MB Form Factor: DIMM Set: None Locator: A2 Bank Locator: Bank4/5 Type: DDR Type Detail: Synchronous Speed: 400 MHz Manufacturer: None Serial Number: None Asset Tag: None Part Number: None Handle 0x003D, DMI type 17, 27 bytes Memory Device Array Handle: 0x0039 Error Information Handle: Not Provided Total Width: 144 bits Data Width: 128 bits Size: 2048 MB Form Factor: DIMM Set: None Locator: A3 Bank Locator: Bank6/7 Type: DDR Type Detail: Synchronous Speed: 400 MHz Manufacturer: None Serial Number: None Asset Tag: None Part Number: None Handle 0x003E, DMI type 17, 27 bytes Memory Device Array Handle: 0x0039 Error Information Handle: Not Provided Total Width: 144 bits Data Width: 128 bits Size: 16384 MB Form Factor: DIMM Set: None Locator: A4 Bank Locator: Bank8/9 Type: DDR Type Detail: Synchronous Speed: 400 MHz Manufacturer: None Serial Number: None Asset Tag: None Part Number: None Handle 0x003F, DMI type 17, 27 bytes Memory Device Array Handle: 0x0039 Error Information Handle: Not Provided Total Width: 144 bits Data Width: 128 bits Size: 16384 MB Form Factor: DIMM Set: None Locator: A5 Bank Locator: Bank10/11 Type: DDR Type Detail: Synchronous Speed: 400 MHz Manufacturer: None Serial Number: None Asset Tag: None Part Number: None
最后两个显示为16384MB，应该是2048MB
我还设置了lm_sensors + i2c-tools：
decode-dimms # decode-dimms version 5929 (2011-02-16 14:58:38 +0100) Memory Serial Presence Detect Decoder By Philip Edelbrock, Christian Zuckschwerdt, Burkart Lingner, Jean Delvare, Trent Piepho and others Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/2-0050 Guessing DIMM is in bank 1 ---=== SPD EEPROM Information ===--- EEPROM Checksum of bytes 0-62 OK (0xE2) # of bytes written to SDRAM EEPROM 128 Total number of bytes in EEPROM 256 Fundamental Memory type DDR SDRAM SPD Revision 1.0 ---=== Memory Characteristics ===--- Maximum module speed 400MHz (PC3200) Size 2048 MB Voltage Interface Level SSTL 2.5V Module Configuration Type ECC Refresh Rate Reduced (7.8 us) - Self Refresh tCL-tRCD-tRP-tRAS 3-3-3-8 Supported CAS Latencies 3T, 2.5T, 2T Supported CS Latencies 0 Supported WE Latencies 1 Minimum Cycle Time 5 ns at CAS 3 6 ns at CAS 2.5 7.5 ns at CAS 2 Maximum Access Time 0.5 ns at CAS 3 0.5 ns at CAS 2.5 0.5 ns at CAS 2 Module Height 1.125" to 1.25" ---=== Manufacturing Information ===--- Manufacturer Infineon (former Siemens) Manufacturing Location Code V Part Number 72D256220GBR5B Revision Code 0x030C Manufacturing Date 2006-W01 Assembly Serial Number 0x0600C212 Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/2-0051 Guessing DIMM is in bank 2 ---=== SPD EEPROM Information ===--- EEPROM Checksum of bytes 0-62 OK (0xB5) # of bytes written to SDRAM EEPROM 128 Total number of bytes in EEPROM 256 Fundamental Memory type DDR SDRAM SPD Revision 1.0 ---=== Memory Characteristics ===--- Maximum module speed 400MHz (PC3200) Size 2048 MB Voltage Interface Level SSTL 2.5V Module Configuration Type ECC Refresh Rate Reduced (7.8 us) - Self Refresh tCL-tRCD-tRP-tRAS 3-3-3-8 Supported CAS Latencies 3T, 2.5T Supported CS Latencies 0 Supported WE Latencies 1 Minimum Cycle Time 5 ns at CAS 3 6 ns at CAS 2.5 Maximum Access Time 0.65 ns at CAS 3 0.7 ns at CAS 2.5 ---=== Manufacturing Information ===--- Manufacturer Kingston Manufacturing Location Code 0x04 Part Number Undefined Manufacturing Date 2006-W14 Assembly Serial Number 0x08108AB0 Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/2-0052 Guessing DIMM is in bank 3 ---=== SPD EEPROM Information ===--- EEPROM Checksum of bytes 0-62 OK (0xE2) # of bytes written to SDRAM EEPROM 128 Total number of bytes in EEPROM 256 Fundamental Memory type DDR SDRAM SPD Revision 1.0 ---=== Memory Characteristics ===--- Maximum module speed 400MHz (PC3200) Size 2048 MB Voltage Interface Level SSTL 2.5V Module Configuration Type ECC Refresh Rate Reduced (7.8 us) - Self Refresh tCL-tRCD-tRP-tRAS 3-3-3-8 Supported CAS Latencies 3T, 2.5T, 2T Supported CS Latencies 0 Supported WE Latencies 1 Minimum Cycle Time 5 ns at CAS 3 6 ns at CAS 2.5 7.5 ns at CAS 2 Maximum Access Time 0.5 ns at CAS 3 0.5 ns at CAS 2.5 0.5 ns at CAS 2 Module Height 1.125" to 1.25" ---=== Manufacturing Information ===--- Manufacturer Infineon (former Siemens) Manufacturing Location Code V Part Number 72D256220GBR5B Revision Code 0x030C Manufacturing Date 2006-W01 Assembly Serial Number 0x0600AE27 Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/2-0053 Guessing DIMM is in bank 4 ---=== SPD EEPROM Information ===--- EEPROM Checksum of bytes 0-62 OK (0xB5) # of bytes written to SDRAM EEPROM 128 Total number of bytes in EEPROM 256 Fundamental Memory type DDR SDRAM SPD Revision 1.0 ---=== Memory Characteristics ===--- Maximum module speed 400MHz (PC3200) Size 2048 MB Voltage Interface Level SSTL 2.5V Module Configuration Type ECC Refresh Rate Reduced (7.8 us) - Self Refresh tCL-tRCD-tRP-tRAS 3-3-3-8 Supported CAS Latencies 3T, 2.5T Supported CS Latencies 0 Supported WE Latencies 1 Minimum Cycle Time 5 ns at CAS 3 6 ns at CAS 2.5 Maximum Access Time 0.65 ns at CAS 3 0.7 ns at CAS 2.5 ---=== Manufacturing Information ===--- Manufacturer Kingston Manufacturing Location Code 0x04 Part Number Undefined Manufacturing Date 2006-W14 Assembly Serial Number 0x011046B4 Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/2-0054 Guessing DIMM is in bank 5 ---=== SPD EEPROM Information ===--- EEPROM Checksum of bytes 0-62 OK (0xE2) # of bytes written to SDRAM EEPROM 128 Total number of bytes in EEPROM 256 Fundamental Memory type DDR SDRAM SPD Revision 1.0 ---=== Memory Characteristics ===--- Maximum module speed 400MHz (PC3200) Size 2048 MB Voltage Interface Level SSTL 2.5V Module Configuration Type ECC Refresh Rate Reduced (7.8 us) - Self Refresh tCL-tRCD-tRP-tRAS 3-3-3-8 Supported CAS Latencies 3T, 2.5T, 2T Supported CS Latencies 0 Supported WE Latencies 1 Minimum Cycle Time 5 ns at CAS 3 6 ns at CAS 2.5 7.5 ns at CAS 2 Maximum Access Time 0.5 ns at CAS 3 0.5 ns at CAS 2.5 0.5 ns at CAS 2 Module Height 1.125" to 1.25" ---=== Manufacturing Information ===--- Manufacturer Infineon (former Siemens) Manufacturing Location Code V Part Number 72D256220GBR5B Revision Code 0x030C Manufacturing Date 2006-W01 Assembly Serial Number 0x04048112 Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/2-0055 Guessing DIMM is in bank 6 ---=== SPD EEPROM Information ===--- EEPROM Checksum of bytes 0-62 OK (0xE2) # of bytes written to SDRAM EEPROM 128 Total number of bytes in EEPROM 256 Fundamental Memory type DDR SDRAM SPD Revision 1.0 ---=== Memory Characteristics ===--- Maximum module speed 400MHz (PC3200) Size 2048 MB Voltage Interface Level SSTL 2.5V Module Configuration Type ECC Refresh Rate Reduced (7.8 us) - Self Refresh tCL-tRCD-tRP-tRAS 3-3-3-8 Supported CAS Latencies 3T, 2.5T, 2T Supported CS Latencies 0 Supported WE Latencies 1 Minimum Cycle Time 5 ns at CAS 3 6 ns at CAS 2.5 7.5 ns at CAS 2 Maximum Access Time 0.5 ns at CAS 3 0.5 ns at CAS 2.5 0.5 ns at CAS 2 Module Height 1.125" to 1.25" ---=== Manufacturing Information ===--- Manufacturer Infineon (former Siemens) Manufacturing Location Code V Part Number 72D256220GBR5B Revision Code 0x030C Manufacturing Date 2006-W01 Assembly Serial Number 0x0600BA20 Number of SDRAM DIMMs detected and decoded: 6
这里全部有2048MB并且被检测到（EEprom字节0-62的校验和都是OK）
我会在晚上发布一个memtest
感谢您的任何提示
编辑：当然，我在64位的centos：
uname -r 2.6.32-71.el6.x86-64
如果在POST时只显示8GB，那么这不是一个CentOS问题。 在升级过程中巧合地发生了与硬件有关的事情，或者前一阵子发生了什么事情，而您没有注意到。
您应该检查以确保您正在运行硬件的最新BIOS版本。 如果这个不足，你应该联系他们寻求支持。