Beyond the File System: Designing Large-Scale File Storage and Serving

Slide 1: Beyond the File System Designing Large Scale File Storage and Serving Cal Henderson

Slide 2: Hello! Web 2.0 Expo, 17 April 2007 2

Slide 3: Big file systems? • Too vague! • What is a file system? • What constitutes big? • Some requirements would be nice Web 2.0 Expo, 17 April 2007 3

Slide 4: 1 Scalable Looking at storage and serving infrastructures Web 2.0 Expo, 17 April 2007 4

Slide 5: 2 Reliable Looking at redundancy, failure rates, on the fly changes Web 2.0 Expo, 17 April 2007 5

Slide 6: 3 Cheap Looking at upfront costs, TCO and lifetimes Web 2.0 Expo, 17 April 2007 6

Slide 7: Four buckets Storage Serving BCP Cost Web 2.0 Expo, 17 April 2007 7

Slide 8: Storage Web 2.0 Expo, 17 April 2007 8

Slide 9: The storage stack File protocol NFS, CIFS, SMB File system ext, reiserFS, NTFS Block protocol SCSI, SATA, FC RAID Mirrors, Stripes Hardware Disks and stuff Web 2.0 Expo, 17 April 2007 9

Slide 10: Hardware overview The storage scale Lower Higher Internal DAS SAN NAS Web 2.0 Expo, 17 April 2007 10

Slide 11: Internal storage • A disk in a computer – SCSI, IDE, SATA • 4 disks in 1U is common • 8 for half depth boxes Web 2.0 Expo, 17 April 2007 11

Slide 12: DAS Direct attached storage Disk shelf, connected by SCSI/SATA HP MSA30 – 14 disks in 3U Web 2.0 Expo, 17 April 2007 12

Slide 13: SAN • Storage Area Network • Dumb disk shelves • Clients connect via a ‘fabric’ • Fibre Channel, iSCSI, Infiniband – Low level protocols Web 2.0 Expo, 17 April 2007 13

Slide 14: NAS • Network Attached Storage • Intelligent disk shelf • Clients connect via a network • NFS, SMB, CIFS – High level protocols Web 2.0 Expo, 17 April 2007 14

Slide 15: Of course, it’s more confusing than that Web 2.0 Expo, 17 April 2007 15

Slide 16: Meet the LUN • Logical Unit Number • A slice of storage space • Originally for addressing a single drive: – c1t2d3 – Controller, Target, Disk (Slice) • Now means a virtual partition/volume – LVM, Logical Volume Management Web 2.0 Expo, 17 April 2007 16

Slide 17: NAS vs SAN With a SAN, a single host (initiator) owns a single LUN/volume With NAS, multiple hosts own a single LUN/volume NAS head – NAS access to a SAN Web 2.0 Expo, 17 April 2007 17

Slide 18: SAN Advantages Virtualization within a SAN offers some nice features: • Real-time LUN replication • Transparent backup • SAN booting for host replacement Web 2.0 Expo, 17 April 2007 18

Slide 19: Some Practical Examples • There are a lot of vendors • Configurations vary • Prices vary wildly • Let’s look at a couple – Ones I happen to have experience with – Not an endorsement ;) Web 2.0 Expo, 17 April 2007 19

Slide 20: NetApp Filers Heads and shelves, up to 500TB in 6 Cabs FC SAN with 1 or 2 NAS heads Web 2.0 Expo, 17 April 2007 20

Slide 21: Isilon IQ • 2U Nodes, 3-96 nodes/cluster, 6-600 TB • FC/InfiniBand SAN with NAS head on each node Web 2.0 Expo, 17 April 2007 21

Slide 22: Scaling Vertical vs Horizontal Web 2.0 Expo, 17 April 2007 22

Slide 23: Vertical scaling • Get a bigger box • Bigger disk(s) • More disks • Limited by current tech – size of each disk and total number in appliance Web 2.0 Expo, 17 April 2007 23

Slide 24: Horizontal scaling • Buy more boxes • Add more servers/appliances • Scales forever* *sort of Web 2.0 Expo, 17 April 2007 24

Slide 25: Storage scaling approaches • Four common models: • Huge FS • Physical nodes • Virtual nodes • Chunked space Web 2.0 Expo, 17 April 2007 25

Slide 26: Huge FS • Create one giant volume with growing space – Sun’s ZFS – Isilon IQ • Expandable on-the-fly? • Upper limits – Always limited somewhere Web 2.0 Expo, 17 April 2007 26

Slide 27: Huge FS • Pluses – Simple from the application side – Logically simple – Low administrative overhead • Minuses – All your eggs in one basket – Hard to expand – Has an upper limit Web 2.0 Expo, 17 April 2007 27

Slide 28: Physical nodes • Application handles distribution to multiple physical nodes – Disks, Boxes, Appliances, whatever • One ‘volume’ per node • Each node acts by itself • Expandable on-the-fly – add more nodes • Scales forever Web 2.0 Expo, 17 April 2007 28

Slide 29: Physical Nodes • Pluses – Limitless expansion – Easy to expand – Unlikely to all fail at once • Minuses – Many ‘mounts’ to manage – More administration Web 2.0 Expo, 17 April 2007 29

Slide 30: Virtual nodes • Application handles distribution to multiple virtual volumes, contained on multiple physical nodes • Multiple volumes per node • Flexible • Expandable on-the-fly – add more nodes • Scales forever Web 2.0 Expo, 17 April 2007 30

Slide 31: Virtual Nodes • Pluses – Limitless expansion – Easy to expand – Unlikely to all fail at once – Addressing is logical, not physical – Flexible volume sizing, consolidation • Minuses – Many ‘mounts’ to manage – More administration Web 2.0 Expo, 17 April 2007 31

Slide 32: Chunked space • Storage layer writes parts of files to different physical nodes • A higher-level RAID striping • High performance for large files – read multiple parts simultaneously Web 2.0 Expo, 17 April 2007 32

Slide 33: Chunked space • Pluses – High performance – Limitless size • Minuses – Conceptually complex – Can be hard to expand on the fly – Can’t manually poke it Web 2.0 Expo, 17 April 2007 33

Slide 34: Real Life Case Studies Web 2.0 Expo, 17 April 2007 34

Slide 35: GFS – Google File System • Developed by … Google • Proprietary • Everything we know about it is based on talks they’ve given • Designed to store huge files for fast access Web 2.0 Expo, 17 April 2007 35

Slide 36: GFS – Google File System • Single ‘Master’ node holds metadata – SPF – Shadow master allows warm swap • Grid of ‘chunkservers’ – 64bit filenames – 64 MB file chunks Web 2.0 Expo, 17 April 2007 36

Slide 37: GFS – Google File System Master 1(a) 2(a) 1(b) Web 2.0 Expo, 17 April 2007 37

Slide 38: GFS – Google File System • Client reads metadata from master then file parts from multiple chunkservers • Designed for big files (>100MB) • Master server allocates access leases • Replication is automatic and self repairing – Synchronously for atomicity Web 2.0 Expo, 17 April 2007 38

Slide 39: GFS – Google File System • Reading is fast (parallelizable) – But requires a lease • Master server is required for all reads and writes Web 2.0 Expo, 17 April 2007 39

Slide 40: MogileFS – OMG Files • Developed by Danga / SixApart • Open source • Designed for scalable web app storage Web 2.0 Expo, 17 April 2007 40

Slide 41: MogileFS – OMG Files • Single metadata store (MySQL) – MySQL Cluster avoids SPF • Multiple ‘tracker’ nodes locate files • Multiple ‘storage’ nodes store files Web 2.0 Expo, 17 April 2007 41

Slide 42: MogileFS – OMG Files Tracker MySQL Tracker Web 2.0 Expo, 17 April 2007 42

Slide 43: MogileFS – OMG Files • Replication of file ‘classes’ happens transparently • Storage nodes are not mirrored – replication is piecemeal • Reading and writing go through trackers, but are performed directly upon storage nodes Web 2.0 Expo, 17 April 2007 43

Slide 44: Flickr File System • Developed by Flickr • Proprietary • Designed for very large scalable web app storage Web 2.0 Expo, 17 April 2007 44

Slide 45: Flickr File System • No metadata store – Deal with it yourself • Multiple ‘StorageMaster’ nodes • Multiple storage nodes with virtual volumes Web 2.0 Expo, 17 April 2007 45

Slide 46: Flickr File System SM SM SM Web 2.0 Expo, 17 April 2007 46

Slide 47: Flickr File System • Metadata stored by app – Just a virtual volume number – App chooses a path • Virtual nodes are mirrored – Locally and remotely • Reading is done directly from nodes Web 2.0 Expo, 17 April 2007 47

Slide 48: Flickr File System • StorageMaster nodes only used for write operations • Reading and writing can scale separately Web 2.0 Expo, 17 April 2007 48

Slide 49: Amazon S3 • A big disk in the sky • Multiple ‘buckets’ • Files have user-defined keys • Data + metadata Web 2.0 Expo, 17 April 2007 49

Slide 50: Amazon S3 Servers Amazon Web 2.0 Expo, 17 April 2007 50

Slide 51: Amazon S3 Servers Amazon Users Web 2.0 Expo, 17 April 2007 51

Slide 52: The cost • Fixed price, by the GB • Store: $0.15 per GB per month • Serve: $0.20 per GB Web 2.0 Expo, 17 April 2007 52

Slide 53: The cost S3 Web 2.0 Expo, 17 April 2007 53

Slide 54: The cost S3 Regular Bandwidth Web 2.0 Expo, 17 April 2007 54

Slide 55: End costs • ~$2k to store 1TB for a year • ~$63 a month for 1Mb • ~$65k a month for 1Gb Web 2.0 Expo, 17 April 2007 55

Slide 56: Serving Web 2.0 Expo, 17 April 2007 56

Slide 57: Serving files Serving files is easy! Disk Apache Web 2.0 Expo, 17 April 2007 57

Slide 58: Serving files Scaling is harder Disk Apache Disk Apache Disk Apache Web 2.0 Expo, 17 April 2007 58

Slide 59: Serving files • This doesn’t scale well • Primary storage is expensive – And takes a lot of space • In many systems, we only access a small number of files most of the time Web 2.0 Expo, 17 April 2007 59

Slide 60: Caching • Insert caches between the storage and serving nodes • Cache frequently accessed content to reduce reads on the storage nodes • Software (Squid, mod_cache) • Hardware (Netcache, Cacheflow) Web 2.0 Expo, 17 April 2007 60

Slide 61: Why it works • Keep a smaller working set • Use faster hardware – Lots of RAM – SCSI – Outer edge of disks (ZCAV) • Use more duplicates – Cheaper, since they’re smaller Web 2.0 Expo, 17 April 2007 61

Slide 62: Two models • Layer 4 – ‘Simple’ balanced cache – Objects in multiple caches – Good for few objects requested many times • Layer 7 – URL balances cache – Objects in a single cache – Good for many objects requested a few times Web 2.0 Expo, 17 April 2007 62

Slide 63: Replacement policies • LRU – Least recently used • GDSF – Greedy dual size frequency • LFUDA – Least frequently used with dynamic aging • All have advantages and disadvantages • Performance varies greatly with each Web 2.0 Expo, 17 April 2007 63

Slide 64: Cache Churn • How long do objects typically stay in cache? • If it gets too short, we’re doing badly – But it depends on your traffic profile • Make the cached object store larger Web 2.0 Expo, 17 April 2007 64

Slide 65: Problems • Caching has some problems: – Invalidation is hard – Replacement is dumb (even LFUDA) • Avoiding caching makes your life (somewhat) easier Web 2.0 Expo, 17 April 2007 65

Slide 66: CDN – Content Delivery Network • Akamai, Savvis, Mirror Image Internet, etc • Caches operated by other people – Already in-place – In lots of places • GSLB/DNS balancing Web 2.0 Expo, 17 April 2007 66

Slide 67: Edge networks Origin Web 2.0 Expo, 17 April 2007 67

Slide 68: Edge networks Cache Cache Cache Origin Cache Cache Cache Cache Cache Web 2.0 Expo, 17 April 2007 68

Slide 69: CDN Models • Simple model – You push content to them, they serve it • Reverse proxy model – You publish content on an origin, they proxy and cache it Web 2.0 Expo, 17 April 2007 69

Slide 70: CDN Invalidation • You don’t control the caches – Just like those awful ISP ones • Once something is cached by a CDN, assume it can never change – Nothing can be deleted – Nothing can be modified Web 2.0 Expo, 17 April 2007 70

Slide 71: Versioning • When you start to cache things, you need to care about versioning – Invalidation & Expiry – Naming & Sync Web 2.0 Expo, 17 April 2007 71

Slide 72: Cache Invalidation • If you control the caches, invalidation is possible • But remember ISP and client caches • Remove deleted content explicitly – Avoid users finding old content – Save cache space Web 2.0 Expo, 17 April 2007 72

Slide 73: Cache versioning • Simple rule of thumb: – If an item is modified, change its name (URL) • This can be independent of the file system! Web 2.0 Expo, 17 April 2007 73

Slide 74: Virtual versioning • Database indicates version 3 of file Version 3 • Web app writes version number into URL example.com/foo_3.jpg • Request comes through Cached: foo_3.jpg cache and is cached with the versioned URL foo_3.jpg -> foo.jpg • mod_rewrite converts versioned URL to path Web 2.0 Expo, 17 April 2007 74

Slide 75: Authentication • Authentication inline layer – Apache / perlbal • Authentication sideline – ICP (CARP/HTCP) • Authentication by URL – FlickrFS Web 2.0 Expo, 17 April 2007 75

Slide 76: Auth layer • Authenticator sits between client and Authenticator storage • Typically built into the Cache cache software Origin Web 2.0 Expo, 17 April 2007 76

Slide 77: Auth sideline Cache Origin Authenticator • Authenticator sits beside the cache • Lightweight protocol used for authenticator Web 2.0 Expo, 17 April 2007 77

Slide 78: Auth by URL Web Server Cache Origin • Someone else performs authentication and gives URLs to client (typically the web app) • URLs hold the ‘keys’ for accessing files Web 2.0 Expo, 17 April 2007 78

Slide 79: BCP Web 2.0 Expo, 17 April 2007 79

Slide 80: Business Continuity Planning • How can I deal with the unexpected? – The core of BCP • Redundancy • Replication Web 2.0 Expo, 17 April 2007 80

Slide 81: Reality • On a long enough timescale, anything that can fail, will fail • Of course, everything can fail • True reliability comes only through redundancy Web 2.0 Expo, 17 April 2007 81

Slide 82: Reality • Define your own SLAs • How long can you afford to be down? • How manual is the recovery process? • How far can you roll back? • How many $node boxes can fail at once? Web 2.0 Expo, 17 April 2007 82

Slide 83: Failure scenarios • Disk failure • Storage array failure • Storage head failure • Fabric failure • Metadata node failure • Power outage • Routing outage Web 2.0 Expo, 17 April 2007 83

Slide 84: Reliable by design • RAID avoids disk failures, but not head or fabric failures • Duplicated nodes avoid host and fabric failures, but not routing or power failures • Dual-colo avoids routing and power failures, but may need duplication too Web 2.0 Expo, 17 April 2007 84

Slide 85: Tend to all points in the stack • Going dual-colo: great • Taking a whole colo offline because of a single failed disk: bad • We need a combination of these Web 2.0 Expo, 17 April 2007 85

Slide 86: Recovery times • BCP is not just about continuing when things fail • How can we restore after they come back? • Host and colo level syncing – replication queuing • Host and colo level rebuilding Web 2.0 Expo, 17 April 2007 86

Slide 87: Reliable Reads & Writes • Reliable reads are easy – 2 or more copies of files • Reliable writes are harder – Write 2 copies at once – But what do we do when we can’t write to one? Web 2.0 Expo, 17 April 2007 87

Slide 88: Dual writes • Queue up data to be written – Where? – Needs itself to be reliable • Queue up journal of changes – And then read data from the disk whose write succeeded • Duplicate whole volume after failure – Slow! Web 2.0 Expo, 17 April 2007 88

Slide 89: Cost Web 2.0 Expo, 17 April 2007 89

Slide 90: Judging cost • Per GB? • Per GB upfront and per year • Not as simple as you’d hope – How about an example Web 2.0 Expo, 17 April 2007 90

Slide 91: Hardware costs Single Cost Cost of hardware Usable GB Web 2.0 Expo, 17 April 2007 91

Slide 92: Power costs Recurring Cost Cost of power per year Usable GB Web 2.0 Expo, 17 April 2007 92

Slide 93: Power costs Single Cost Power installation cost Usable GB Web 2.0 Expo, 17 April 2007 93

Slide 94: Space costs Recurring Cost ] [ Cost per U x U’s needed (inc network) Usable GB Web 2.0 Expo, 17 April 2007 94

Slide 95: Network costs Single Cost Cost of network gear Usable GB Web 2.0 Expo, 17 April 2007 95

Slide 96: Misc costs Single & Recurring Costs ] [ Support contracts + spare disks + bus adaptors + cables Usable GB Web 2.0 Expo, 17 April 2007 96

Slide 97: Human costs Recurring Cost ] [ Admin cost per node x Node count Usable GB Web 2.0 Expo, 17 April 2007 97

Slide 98: TCO • Total cost of ownership in two parts – Upfront – Ongoing • Architecture plays a huge part in costing – Don’t get tied to hardware – Allow heterogeneity – Move with the market Web 2.0 Expo, 17 April 2007 98

Slide 99: (fin)

Slide 100: Photo credits • flickr.com/photos/ebright/260823954/ • flickr.com/photos/thomashawk/243477905 / • flickr.com/photos/tom-carden/116315962/ • flickr.com/photos/sillydog/287354869/ • flickr.com/photos/foreversouls/131972916/ • flickr.com/photos/julianb/324897/ • flickr.com/photos/primejunta/140957047/ • flickr.com/photos/whatknot/28973703/ • flickr.com/photos/dcjohn/85504455/ Web 2.0 Expo, 17 April 2007 100

Slide 101: You can find these slides online: iamcal.com/talks/ Web 2.0 Expo, 17 April 2007 101