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Почему низкая производительность SSD в Centos 7?

Решил замерить производительность ssd (Samsung SSD 840 EVO 250GB)
На диске находится ОС

Результаты:
[root@localhost test]# hdparm -t /dev/sde
/dev/sde:
Timing buffered disk reads: 146 MB in 3.17 seconds = 46.04 MB/sec

Теперь вопрос: почему такая низкая производительность и куда копать?

OS: CentOS Linux release 7.2.1511 (Core)

[root@localhost test]# fdisk -l /dev/sde
WARNING: fdisk GPT support is currently new, and therefore in an experimental phase. Use at your own discretion.
Disk /dev/sde: 250.1 GB, 250059350016 bytes, 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 label type: gpt
# Start End Size Type Name
1 2048 2000895 976M EFI System EFI System Partition
2 2000896 2975743 476M Microsoft basic
3 2975744 488396799 231,5G Linux LVM

[root@localhost test]# hdparm -I /dev/sde

/dev/sde:

ATA device, with non-removable media
Model Number: Samsung SSD 840 EVO 250GB
Serial Number: S1DBNSBF151834F
Firmware Revision: EXT0BB6Q
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
* unknown 76[15]
* DMA Setup Auto-Activate optimization
Device-initiated interface power management
* Asynchronous notification (eg. media change)
* Software settings preservation
* 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: 50025388a01e2b6b
NAA : 5
IEEE OUI : 002538
Unique ID : 8a01e2b6b
Checksum: correct
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Ответы на вопрос 2
По умолчанию в Centos 7 работает дисковый планировщик Elevator, который хорошо заточен под дисковые накопители и не очень под твердотельные.
Надо переключить на планировщик Deadline, который хорошо заточен под SSD.
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Можно попробовать выполнить "Trim":
fstrim --all
Если поможет, можно поставить эту комманду в crontab.
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