Vector Search -An Introduction in Oracle Database 23ai.pptx
Why 4k?
1. Why 4K?
October 2, 2012
George Wilson
george.wilson@delphix.com
2. Why 4K? (Not Y4K)
● This is not the next Millennium bug!
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3. Storage History
● 1998 IBM publishes a paper proposing an increase of disk
sector size from 512B to 4K
● 2000 4K IDEMA (International Disk Drive Equipment and
Materials Association) committee was formed
● 2005 ZFS released in OpenSolaris with support for block sizes
ranging from 512B to 128K
● 2005 512B emulation mode proposed, later known as AF
512e
● 2006 ZFS adds large sector support
● 2009 Advanced Format is approved as naming convention
for 4K sectors
● 2011 All hard drive manufactures start to ship AF 512e drives
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4. Advanced Format Drives
● Two flavors of Advanced Format Drives
○ AF 512e - Advanced Format 512B Emulation
○ AF 4Kn - Advanced Format 4K Native
Today
Future
(2012?)
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5. Advanced Format 512e (AF 512e)
● Maps 8 512B logical blocks
into 1 physical 4K block
● Provides an emulation layer
for compatibility
0 1 2 3 4 5 6 7 512B Logical Blocks
4K Physical Block #0 4K Physical Blocks
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6. Predicting Future Problems
"Access on a 512-byte basis would continue to be
supported, but performance would be inferior to
that in which access is done on a 4096-byte basis,
and might well be inferior to that of previous
drives with 512-byte native block size." -- Large
Block Size by Paul Hodges and David Cheng, 1998
7. Problems in a 4K World
● Lies
○ AF 512e Drive lie about their physical block size
○ LUNs from storage vendors lie about their physical block
size
● Misaligned I/O
○ Proper partitioning
○ Some AF 512e drives provide an XP jumper (XP partition
starts on sector 63, not 4K aligned)
● Read-modify-write
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11. Solutions (sort of)
● Override the lies from the device
○ FreeBSD, Illumos, and Linux have all implemented a way
to override the discovered sector size
○ FreeBSD
■ using gnop to create 4k device
○ Illumos
■ add an override into sd.conf:
sd-config-list = "VENDOR PRODUCT", physical-block-size:4096;
○ Linux
■ zpool create -o ashift=12 tank <device>
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12. Drawbacks of 4K and ZFS
● Reduced compression ratio
○ Blocks less than 4K mean 0% compression
○ 8K block can only achieve 50% compression
● Migrating drives from 512B to 4K
● Inefficient metadata allocation
○ Some metadata is allocated in 4K chunks and will no
longer get compressed
● Improper accounting of compressed sizes in datasets
● RAID-Z and 4k -- not recommended
● Configuring root pools to use 4K
○ Grub support?
● Fewer uberblocks Delphix Proprietary and Confidential
13. Q&A / Beer?
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14. ZFS Day
October 2, 2012
George Wilson
george.wilson@delphix.com
