BTRFS
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Aquest article no pretén substituir al manual oficial, sols és, de moment, una recopilació de apunts a partir de l'ús del sistema de fitxers.
BTRFS es compara sovint amb ZFS, ja que existeixen per les mateixes raons. La primera diferència és la forma en que han arribat a Linux i els problemes de llicències que pot donar. ZFS és més madur i,en la majoria de casos més robust. BTRFS és més flexible en algunes coses.
Avantatges experimentats per mí de BTRFS sobre ZFS:
- Més fàcil de crear i de muntar els volums creats.
- Si afegeixes un nou disc a un RAID1, per exemple, en ZFS sols el sincronitza en els nous arxius. En BTRFS es sincronitza si vols.
- BTRFS funciona dins de contenedors LXD, per tant, si fem nesting podem aprofitar els avantatges dins dels subcontenidors.
Cas pràctic
En un servidor configurat com a RAID 10 amb 4 discs durs, trobem un misstage a la pantalla que diu:
BTRFS error (device sda1): bdev /dev/sdf1 errs: wr 51956436, rd 28739183, flush 124601, corrupt 0, gen 0
Això ens diu que hi ha algun problema en el sistema d'arxius. Si fem algunes comprovacions:
sudo btrfs scrub start /media/btrfs/ scrub started on /media/btrfs/, fsid bb600f14-9fbb-4f27-af33-95c6ac1975fe (pid=16546)
sudo btrfs scrub status /media/btrfs/ scrub status for bb600f14-9fbb-4f27-af33-95c6ac1975fe scrub started at Mon Nov 18 13:54:43 2019, running for 00:15:05 total bytes scrubbed: 84.04GiB with 5340488 errors error details: read=5340485 super=3 corrected errors: 0, uncorrectable errors: 5340485, unverified errors: 0
Efectivament, es troben molts errors que no pot solucionar.
Si fem un smartctl al disc que sembla fallar:
sudo smartctl /dev/sdf -a
smartctl 6.6 2016-05-31 r4324 [x86_64-linux-4.15.0-70-generic] (local build)
Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org
=== START OF INFORMATION SECTION ===
Model Family: Seagate Barracuda 7200.14 (AF)
Device Model: ST2000DM001-1ER164
Serial Number: W4Z19BCP
LU WWN Device Id: 5 000c50 07d44b288
Firmware Version: CC25
User Capacity: 2.000.398.934.016 bytes [2,00 TB]
Sector Sizes: 512 bytes logical, 4096 bytes physical
Rotation Rate: 7200 rpm
Form Factor: 3.5 inches
Device is: In smartctl database [for details use: -P show]
ATA Version is: ACS-2, ACS-3 T13/2161-D revision 3b
SATA Version is: SATA 3.1, 6.0 Gb/s (current: 3.0 Gb/s)
Local Time is: Mon Nov 18 15:53:14 2019 UTC
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: (0x82) Offline data collection activity
was completed without error.
Auto Offline Data Collection: Enabled.
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: ( 89) seconds.
Offline data collection
capabilities: (0x7b) SMART execute Offline immediate.
Auto Offline data collection on/off 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: ( 219) minutes.
Conveyance self-test routine
recommended polling time: ( 2) minutes.
SCT capabilities: (0x1085) SCT Status supported.
SMART Attributes Data Structure revision number: 10
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE
1 Raw_Read_Error_Rate 0x000f 117 099 006 Pre-fail Always - 162249504
3 Spin_Up_Time 0x0003 100 096 000 Pre-fail Always - 0
4 Start_Stop_Count 0x0032 100 100 020 Old_age Always - 175
5 Reallocated_Sector_Ct 0x0033 100 100 010 Pre-fail Always - 0
7 Seek_Error_Rate 0x000f 079 060 030 Pre-fail Always - 89979761
9 Power_On_Hours 0x0032 081 081 000 Old_age Always - 16693
10 Spin_Retry_Count 0x0013 100 100 097 Pre-fail Always - 0
12 Power_Cycle_Count 0x0032 100 100 020 Old_age Always - 85
183 Runtime_Bad_Block 0x0032 100 100 000 Old_age Always - 0
184 End-to-End_Error 0x0032 100 100 099 Old_age Always - 0
187 Reported_Uncorrect 0x0032 100 100 000 Old_age Always - 0
188 Command_Timeout 0x0032 100 089 000 Old_age Always - 1 2 12
189 High_Fly_Writes 0x003a 099 099 000 Old_age Always - 1
190 Airflow_Temperature_Cel 0x0022 064 048 045 Old_age Always - 36 (Min/Max 30/38)
191 G-Sense_Error_Rate 0x0032 100 100 000 Old_age Always - 0
192 Power-Off_Retract_Count 0x0032 100 100 000 Old_age Always - 44
193 Load_Cycle_Count 0x0032 067 067 000 Old_age Always - 67287
194 Temperature_Celsius 0x0022 036 052 000 Old_age Always - 36 (0 9 0 0 0)
197 Current_Pending_Sector 0x0012 100 100 000 Old_age Always - 0
198 Offline_Uncorrectable 0x0010 100 100 000 Old_age Offline - 0
199 UDMA_CRC_Error_Count 0x003e 200 069 000 Old_age Always - 262
240 Head_Flying_Hours 0x0000 100 253 000 Old_age Offline - 16485h+48m+15.949s
241 Total_LBAs_Written 0x0000 100 253 000 Old_age Offline - 19632474908
242 Total_LBAs_Read 0x0000 100 253 000 Old_age Offline - 1261379460714
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]
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.
Diu que no està molt sà, però que funciona. Per tant, cal intentar reparar el sistema d'arxius:
btrfs rescue zero-log /dev/sdf1 # Si és un error de transaccions tallades per un tall elèctric, per exemple. btrfs rescue super-recover # Si no està el superblock, el recupera de una de les còpies que té el disc. btrfs rescue chunk-recover # En cas de fallar les metadates i tindre fitxers desconeguts. És lent i perillós. btrfs check --repair /dev/sdXY # Per reparar el sistema d'arxius.