I grabbed an Intel S3700 to use for SLOG kind of workload. I understand that write sync performance (fsync() latency) is the most important factor here. Did a quick pg_test_fsync run and found that fsync() latency is almost 8ms each write sync.
This is very different from what I heard previously on this forum, e.g. in the thread below, BackupProphet had 50x better latency on his S3710.
https://forums.servethehome.com/index.php?threads/inexpensive-ssd-for-slog-device.13889/
Any idea what might went wrong? Thanks
I am running on Ubuntu 16.04 with 4.15 kernel, my mount options are
5 seconds per test
O_DIRECT supported on this platform for open_datasync and open_sync.
Compare file sync methods using one 8kB write:
(in wal_sync_method preference order, except fdatasync is Linux's default)
open_datasync 5738.493 ops/sec 174 usecs/op
fdatasync 5719.920 ops/sec 175 usecs/op
fsync 125.104 ops/sec 7993 usecs/op
fsync_writethrough n/a
open_sync 120.013 ops/sec 8332 usecs/op
Compare file sync methods using two 8kB writes:
(in wal_sync_method preference order, except fdatasync is Linux's default)
open_datasync 2864.313 ops/sec 349 usecs/op
fdatasync 4365.294 ops/sec 229 usecs/op
fsync 128.987 ops/sec 7753 usecs/op
fsync_writethrough n/a
open_sync 60.073 ops/sec 16646 usecs/op
This is very different from what I heard previously on this forum, e.g. in the thread below, BackupProphet had 50x better latency on his S3710.
https://forums.servethehome.com/index.php?threads/inexpensive-ssd-for-slog-device.13889/
Any idea what might went wrong? Thanks
I am running on Ubuntu 16.04 with 4.15 kernel, my mount options are
smartctl -a output attached belowrw,relatime,errors=panic,max_batch_time=0,data=ordered
=== START OF INFORMATION SECTION ===
Model Family: Intel 730 and DC S35x0/3610/3700 Series SSDs
Device Model: INTEL SSDSC2BA400G3
Serial Number: BTTV248200S3400HGN
LU WWN Device Id: 5 001517 8f3593b61
Firmware Version: 5DV12270
User Capacity: 400,088,457,216 bytes [400 GB]
Sector Sizes: 512 bytes logical, 4096 bytes physical
Rotation Rate: Solid State Device
Form Factor: 2.5 inches
Device is: In smartctl database [for details use: -P show]
ATA Version is: ACS-2 T13/2015-D revision 3
SATA Version is: SATA 2.6, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is: Fri Jan 25 19:29:12 2019 CST
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: (0x02) Offline data collection activity
was completed without error.
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: ( 2) seconds.
Offline data collection
capabilities: (0x79) SMART execute Offline immediate.
No Auto Offline data collection support.
Suspend Offline collection upon new
command.
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: ( 2) minutes.
Conveyance self-test routine
recommended polling time: ( 2) 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: 1
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE
5 Reallocated_Sector_Ct 0x0032 100 100 000 Old_age Always - 0
9 Power_On_Hours 0x0032 100 100 000 Old_age Always - 15
12 Power_Cycle_Count 0x0032 100 100 000 Old_age Always - 13
170 Available_Reservd_Space 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
174 Unsafe_Shutdown_Count 0x0032 100 100 000 Old_age Always - 9
175 Power_Loss_Cap_Test 0x0033 100 100 010 Pre-fail Always - 619 (1 21)
183 SATA_Downshift_Count 0x0032 100 100 000 Old_age Always - 0
184 End-to-End_Error 0x0033 100 100 090 Pre-fail Always - 0
187 Reported_Uncorrect 0x0032 100 100 000 Old_age Always - 0
190 Temperature_Case 0x0022 087 087 000 Old_age Always - 13 (Min/Max 13/15)
192 Unsafe_Shutdown_Count 0x0032 100 100 000 Old_age Always - 9
194 Temperature_Internal 0x0022 100 100 000 Old_age Always - 24
197 Current_Pending_Sector 0x0032 100 100 000 Old_age Always - 0
199 CRC_Error_Count 0x003e 100 100 000 Old_age Always - 0
225 Host_Writes_32MiB 0x0032 100 100 000 Old_age Always - 24348
226 Workld_Media_Wear_Indic 0x0032 100 100 000 Old_age Always - 65535
227 Workld_Host_Reads_Perc 0x0032 100 100 000 Old_age Always - 65535
228 Workload_Minutes 0x0032 100 100 000 Old_age Always - 65535
232 Available_Reservd_Space 0x0033 100 100 010 Pre-fail Always - 0
233 Media_Wearout_Indicator 0x0032 100 100 000 Old_age Always - 0
234 Thermal_Throttle 0x0032 100 100 000 Old_age Always - 0/0
241 Host_Writes_32MiB 0x0032 100 100 000 Old_age Always - 24348
242 Host_Reads_32MiB 0x0032 100 100 000 Old_age Always - 24312
SMART Error Log Version: 1
No Errors Logged
SMART Self-test log structure revision number 1
Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error
# 1 Short offline Completed without error 00% 14 -
SMART Selective self-test log data structure revision number 1
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.
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