storage systems: advanced topics learning objectives: to understand major characteristics of ssd to...
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Storage Systems: Storage Systems: Advanced TopicsAdvanced Topics
Learning Objectives:• To understand major characteristics of SSD• To understand Logical Volume Management –
its motivations and its facilities• To understand how Storage Area Networks
extend these features to multiple systems• To relate LVM and SAN to a most modern file
system implementation
COMP25212 1Feb 2013
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Solid State DisksSolid State Disks
• Today’s technology: Flash Memory– Floating gate Field Effect Transistor
COMP25212
• Store {0, 1} on “Floating” gate
- no electrical connectionFeb 2013
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NAND Flash OperationNAND Flash Operation
• No connection to “Floating” gate– Quantum tunneling– Block erase, bit writing– Memory wear (10K writes?)– Multi Level Cell e.g. {0, ¼, ½, ¾} 2 bits/cell– Read disturb
COMP25212Feb 2013
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Flash ControllerFlash Controller
• Implement:– Error Correcting Codes– (Bad) Block Remapping– Write levelling– Read tracking and rewriting
• But note:– 10 year data retention(?)– Wear-out with write cycles– Performance falls as file system fills– Performance falls with device wearout
Feb 2013 COMP25212
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Hard Disks and SSDHard Disks and SSD
Feb 2013 COMP25212
(2013 figures) Hard Disk SSD
Capacity/price 4Tb/£140 250Gb/£125
Streaming reads 205 Mb/s 530 Mb/s
Streaming writes 205 Mb/s 240 Mb/s
Random 4Kb read 15.5 mS 11 uS
Random 4Kb write 6.4 mS 23 uS
Power 6 - 8 W 0.3 - 4.2 W
(eg) Hitachi 7k4000 Samsung SSD 840
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Storage VirtualizationStorage Virtualization
File System Code– assumes 1 file system– to 1 disk drive (partition)
Stripe/Mirror/RAID changes this
Storage Virtualization: break filesystem/drive relationship
COMP25212 6
OSOS
Device DriversDevice Drivers
File SystemFile System
Feb 2013
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Logical Volume Logical Volume ManagementManagement
• Virtual mapping between file system code and physical device
• Analogous (but not identical!) to virtual memory addressing
• “Volume Group” of all drives in a pool• Storage space in “Volume Group” divided
into “Physical Extents” – usually all same size
• “Logical Volume” is set of “Physical Extents”
COMP25212 7Feb 2013
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Logical Volume Logical Volume ManagementManagement
• Mirror/Stripe/RAID provided within LVM layer
• Resize filesystem
• “Snapshot” a live filesystem
COMP25212 8
OSOS
Device DriversDevice Drivers
File SystemFile System
LVM layerLVM layer
Volume Group
Feb 2013
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e.g. Linux Servere.g. Linux Server
• / - mostly read – want fast seeks
• swap – read/write – want high bandwidth
• /opt – infrequent access
• /var – huge, infrequent access
• Mirror /
• Stripe swap
• spare space to /opt and /var
COMP25212 9Feb 2013
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LVM Example:LVM Example:
• Now we can share resources more flexibly and more efficiently – but only on one server
COMP25212 10Feb 2013
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Storage Area Storage Area NetworkingNetworking
• Implement LVM features in separate storage controller
• Connect multiple servers to storage controller• via SCSI, or FibreChannel, or Infiniband, or
…(n.b. SAN over Ethernet is conventionally called Networked Attached Storage (NAS)
• Now can share disk resources across multiple servers
• Rapid migration of disk images
COMP25212 11Feb 2013
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Storage Area Network Storage Area Network ControllerController
COMP25212 12
8 “Blade Servers”
SA
N
Con
trol
ler
SA
N
Con
trol
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Feb 2013
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SAN Key FeaturesSAN Key Features
• Functionality– Key element of “system virtualization”– Migrating virtual machines– “De-duping” – share common subsets of
file systems (think Virtual Machine images!)
• Management:– Manage storage separately from server
physical resources– Maximize flexibility of storage provisioning
COMP25212 13Feb 2013
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ZFS – Volume Aware ZFS – Volume Aware File SystemFile System
Marketing claims:
• Lost a file?
• Run out of space?
• Difficult disk upgrade?
• Want to grow/shrink?
• Data Corruption?
COMP25212 14
Pools of storage
Feb 2013
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ZFS techniquesZFS techniques
• Lost a file?– Copy-on-write – simple rollback/recovery
• Run out of space/Difficult disk upgrade?– Add new storage to live systems– Self-checking, self-healing
• Want to grow/shrink?
• Data Corruption?– end-to-end sumchecking
COMP25212 15Feb 2013
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ZFS ImplementationZFS Implementation
• ZFS Combines File Service and Logical Volume Management
• Is this a good idea?
Discuss
COMP25212 16Feb 2013