Red Hat ENTERPRISE LINUX - ONLINE STORAGE RECONFIGURATION GUIDE BETA Technické informace Strana 37
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Hodnocené. / 5. Na základě hodnocení zákazníků
Chapter 6. The Ext4 File System
The ext4 file system is a scalable extension of the ext3 file system, which was the default file system of
Red Hat Enterprise Linux 5. Ext4 is the default file system of Red Hat Enterprise Linux 6, and can
support files and file systems up to 16 terabytes in size. It also supports an unlimited number of sub-
directories (the ext3 file system only supports up to 32,000), though once the link count exceeds
65,000 it resets to 1 and is no longer increased.
Note
As with ext3, an ext4 volume must be umounted in order to perform an fsck. For more
information, see Chapter 5, The Ext3 File System.
Main Feat u res
Ext4 uses extents (as opposed to the traditional block mapping scheme used by ext2 and
ext3), which improves performance when using large files and reduces metadata overhead
for large files. In addition, ext4 also labels unallocated block groups and inode table
sections accordingly, which allows them to be skipped during a file system check. This
makes for quicker file system checks, which becomes more beneficial as the file system
grows in size.
Allo cat io n Feat u res
The ext4 file system features the following allocation schemes:
Persistent pre-allocation
Delayed allocation
Multi-block allocation
Stripe-aware allocation
Because of delayed allocation and other performance optimizations, ext4's behavior of
writing files to disk is different from ext3. In ext4, when a program writes to the file system, it
is not guaranteed to be on-disk unless the program issues an fsync() call afterwards.
By default, ext3 automatically forces newly created files to disk almost immediately even
without fsync(). This behavior hid bugs in programs that did not use fsync() to ensure
that written data was on-disk. The ext4 file system, on the other hand, often waits several
seconds to write out changes to disk, allowing it to combine and reorder writes for better
disk performance than ext3.
Warning
Unlike ext3, the ext4 file system does not force data to disk on transaction commit. As
such, it takes longer for buffered writes to be flushed to disk. As with any file system,
use data integrity calls such as fsync() to ensure that data is written to permanent
storage.
O t h er Ext 4 Feat u res
The ext4 file system also supports the following:
Red Hat Ent erprise Lin ux 6 St orage Admin ist rat io n G uide
32
- Red Hat Enterprise Linux 6 1
- Storage Administration Guide 1
- Edition 2 3
- Edited by 4
- Legal Notice 5
- Abstract 5
- Table of Contents 6
- 1. Document Convent ions 13
- 1.2. Pull-quot e Convent ions 14
- Important 15
- 2.2. We Need Feedback 16
- Network Block Storage 18
- Part I. File Systems 19
- 2.1.1. FHS Organiz at ion 20
- 2.4. Discard unused blocks 29
- 3.2. Addit ional Informat ion 31
- Chapter 4. Btrfs 32
- Write Barriers 39
- Writ e Barriers 40
- Setting Project Limits 50
- Set t in g Project Limit s 52
- Simple Mode for xfsrest ore 54
- 9.2. pNFS 57
- 9.4. auto fs 59
- 9.7.4 . Host name Format s 73
- 9.7.5. NFS over RDMA 73
- 9.8. Securing NFS 74
- 9.9. NFS and rpcbi nd 76
- Related Books 78
- Chapter 10. FS-Cache 79
- 10.1. Performance Guarant ee 80
- 10.2. Set t ing Up a Cache 80
- 10.3.1. Cache Sharing 81
- Chapt er 1 0 . FS- Cache 82
- 10.6. References 84
- 11.3. Special Considerat ions 87
- Chapter 12. File System Check 90
- 12.2.2. XFS 92
- 12.2.3. Bt rfs 94
- Chapter 13. Partitions 95
- 13.2.3. Add t o /etc/fstab 98
- 13.3. Removing a Part it ion 99
- 13.4 . Resizing a Part it ion 99
- Chapt er 1 3. Part it ions 100
- 14 .1. What is LVM2? 102
- 14 .2.3. Migrat ing Ext ent s 109
- Installed Documentation 118
- Useful Websites 118
- Chapter 15. Swap Space 119
- Chapt er 1 5. Swap Space 120
- 15.2.3. Removing a Swap File 122
- 15.3. Moving Swap Space 123
- Chapter 16. Disk Quotas 124
- Chapt er 1 6 . Disk Q uot as 126
- 16.2. Managing Disk Quot as 128
- 16.3. Disk Quot a References 130
- Firmware RAID 131
- Hardware RAID 131
- Software RAID 132
- 17.3. Linux RAID Subsyst ems 134
- 17.5. Configuring RAID Set s 135
- 18.2.3. Sharing Mount s 142
- 18.4 .2. Useful Websit es 147
- 19.1. Commands 148
- 19.4. vo l ume_key References 152
- 20.1. Mount ing File Syst ems 153
- 20.2. Set t ing Access ACLs 153
- 20.3. Set t ing Default ACLs 154
- 20.4. Ret rieving ACLs 155
- 20.7. ACL References 156
- I/O Scheduler 159
- Virtual Memory 159
- Chapter 22. Write Barriers 160
- How Write Barriers Work 160
- Disabling Write Caches 161
- Battery-Backed Write Caches 161
- High-End Arrays 162
- Block Device ioctls 164
- 23.3. St andards 165
- 23.5. Logical Volume Manager 166
- File System tools 167
- 25.1. Fibre Channel 171
- 25.2. iSCSI 173
- 25.3. Persist ent Naming 175
- 25.3.1. WWID 176
- 25.16.1. Fibre Channel 199
- SCSI Error Handler 201
- Device States 203
- Command Timer 203
- 26.1. Virt ual St orage 205
- 26.2. DM-Mult ipat h 205
- Revision History 207
- Revision Hist ory 208
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