Building a storage WAN for enterprise DR
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Transcript of Building a storage WAN for enterprise DR
BACKUP/MASTER: Building a Storage Wide Area Network (WAN) for Enterprise DR
Dragon Slayer ConsultingMarc Staimer, President & CDS [email protected] 22 September 2004
9/22/2004 Building a Storage WAN for Enterprise DR 2
Dragon Slayer background
7 yrs sales
7 yrs sales mgt
10 yrs mkting & bus dev
• Storage & SANs
• 6 years consulting
Launched or participated
• 20 products
Paid Consulting• > 70 vendors
Unpaid Consulting• > 200 end users
Known Industry Expert• Speak ~ 5 events/yr
• Write ~ 3 trade articles/yr
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Storage DR WAN level setting
Storage WANs by definition
• Primarily for DR purposes
Enterprise DR Characteristics
• Big blocks of data
• Can overwhelm standard IP routers
• Not limited to nights & weekends Time is very relevant
• Time windows are getting smaller
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Classifying DR dataMission-critical = Crucial• Organization’s vital data• Primary business processes, primary applications, &
SLAs• Data access loss often means organizational death
Essential = Secret• Very important to the organization• Day-to-day business processes• Instantaneous recovery preferred & not required
Important = Valuable• Many day-to-day organization ops & apps
Low-critical = Nominal value• Low organizational value
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Prioritizing DR data
Mission-critical = Crucial• eCommerce/order-entry/sales transactions
Essential = Secret• Customer data/intellectual property/Email
Important = Valuable• Employee records/marketing collateral
Low-critical = Nominal value• Resumes/market data/competitive data
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Recovery Point Objectives (RPO)
RPO = point-in-time which systems & data • Must be recovered TO within the DR facility
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Recovery Time Objectives (RTO)
RTO = total time which systems & apps • Must be recovered AFTER an outage
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Picking WAN DR options
Mission critical• Split mirror disk-to-disk• Synch mirroring• Hot standby at remote
locations Servers and storage
• Continuous snapshots
Essential• Asynch remote mirroring• Snapshot• Distributed backup• Volume copy
Important • Wide area backup• Distributed directory
journaling
Low critical • Electronic Tape vaulting
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Wide Area Network (WAN) options
ATM
SONET
TCP/IP
WAN can = > 50% of DR OpEx costs
WAN
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ATMAsynchronous Transfer Mode
Pros
• High performance OC3 to OC48 • 155Mbps to 2.5Gbps
• Shared network (cell based) IP over ATM
• Excellent QoS
• Available from most telcos
• High bandwidth utilization
Cons
• Bandwidth overhead
• Niche technology
• Out-of-favor Disappearing Appears to be Dead-
End
• High cost
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SONET/SDHSynchronous Optical Network/Synchronous Digital Hierarchy
Pros• High performance
OC3 to OC192 • 155Mbps to 10Gbps
• Preferred by most telcos
• Can be shared TCP/IP switch/routers CWDM technology DWDM technology POS (IP packet over SONET)
• Very high bandwidth utilization
Cons• Expensive
Although declining
• Not shareable natively
• Not a LAN technology
• Separate mgt from LAN
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TCP/IPTransmission Control Protocol/Internet Protocol
Pros• Ubiquitous
• Available everywhere
• Well known mgt
• Large knowledge pool
• Shared network
• Std network for most orgs.
• Can piggyback on IP WAN DR WAN perceived as
free
Cons• Designed for packet loss
Typical = ~ 1% Packet loss =
retransmissions• Congestion• Bit Error Rates• Jitter• Latency• Router buffer overruns
Packet loss = low throughput
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Calculating storage WAN bandwidth
How much data between application sites?• And the DR site
Over what period of time to move the data?
Will the bandwidth be shared?• If so, how much bandwidth is available?
What type of WAN?• Native ATM
• Native SONET
• TCP/IP
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Assumptions
ATM• > 80% bandwidth utilization
• IP over ATM
• And native ATM end-to-end
SONET/SDH • a.k.a. clear channel
• > 90% bandwidth utilization
• Primarily POS (IP over SONET)
• Or FCBB (FC over SONET)
TCP/IP • End-to-end
• Packet loss avg = ~ 1%
• < 30% bandwidth utilization Worsens w/distance Worsens w/> packet loss For calculations = 30%
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Market trends
In a poll of over 200 end users
• From SMB, SME, & Enterprise
• 61% = DR over TCP WANs
• 3% = DR over SONET
• 1% = DR over ATM
• 24% = No DR over WAN
• 11% = Both TCP & SONET or ATM
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0/0
20% 20% 20% 20% 20%
1 2 3 4 5
What WAN do you use today for data protection?
1. TCP/IP
2. SONET
3. ATM
4. TCP & SONET or ATM
5. None of the above
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Why TCP/IP WANs are so prevalent with DR
Perception that the bandwidth is free• Or at least very inexpensive
Piggyback on IP WAN networks
Evenings and Weekends
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Most DR apps primarily USE IP
Asynch mirroring
Snapshot
Volume replication
Distributed backup
Incremental
• Replication or Backup
Tape Vaulting
Continuous replication
Continuous snapshot
Fibre Channel over WAN
• FCIP
• iFCP
• Although there is FCBB FC over SONET
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Reality check:Why TCP/IP WAN throughput is dismal
TCP/IP• Byte-streaming protocol moving data in small packets
• Retransmits the data from the last point of the error
• Immediately reduces the rate
• Backs down to slow start mode
• Additional ramp-up packet loss causes further rate reduction
• During periods of “lossy” conditions Application performance never has a chance to
recover
Why packet loss is so detrimental to TCP throughput
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TCP 1985: Designed for LANs
1. TCP Slow Start• Packet rate 2X• Per successful R-T
2. Per Loss Event• Sending rate cut 1/2
3. TCP Congestion Control • Sending rate > 1• Per successful R-T
1
Slow Start
Congestion Control
xx xxxx x
2 3
x x x x
X = packet loss
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TCP 2004: LAN protocol over the WAN
Same internal logic• Since 1985!
1. High BW Loss events • = large packet losses
2. High Latency• Slower recovery • During congestion control
3. Infrequent feedback• Changing route conditions• Based on packet loss events
31
Slow Start
Congestion Control
xx x
2
DS3, 45Mb/s, high latency & loss
X = packet loss
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TCP/IP WAN
TCP resource contention on shared linksreduces data protection throughput
1. Sporadic packet loss2. Short & long distance
sessions • Contend for same
resources3. Router queues
change dynamically • From traffic bursts
3
1
Slow Start
Congestion Control
2xx xxxx x x x x x
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TCP: What really happens to long distance sessions?
1. Packet loss events • Frequent for shared nets
2. Loss events • Router buffer overruns
Affect other sessions Lots of lost packets
3. LD sessions beat down • By SD sessions
4. Results • Low throughput• Random delays
3
1
Slow Start
Long Distance
xx xxxx x
WAN Bandwidth (DS3) 45Mb/s
Short Distance
TCP/IP WAN
2
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The DR TCP WAN disconnect
As distance >, performance <
Worse with higher bandwidth
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DR TCP/IP conclusionPerception & reality do not match• Must be taken into account
• When building a Storage WAN for Enterprise DR
• Increasing the bandwidth doesn’t solve the problem
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Now what?
What happens when:• Throughput is much less than usable bandwidth?
• Time windows can’t be met?
• The IP WAN is insufficient?
• Throwing more bandwidth at it fails to resolve problem?
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There are 2 choices
Go ATM end-to-end• Not very palatable to most end users
OR: TCP enhancers• Proxies
• Compressors
• Caching/spoofing
• Accelerators
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Different clever technologiesTCP/IP performance enhancing proxy• Eliminates TCP packet loss & latency issues
Compression• Increases payloads per packet
Compression increases from 2X to 400X
Caching (a.k.a. spoofing)• Acknowledges packets locally
Accelerators• Resequencing, QoS, concatenation, duplication
elimination
• Chatty protocol elimination
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Shield
TCP/IP network shielding
Data protection packets in a TCP/IP network
Bit Error Rates Network
Jitter
TCP/IPLatency
NetworkCongestion
Shields TCP/IP network
• Bit error rates
• Congestion
• Jitter
• Latency
• Buffer overflows
Much > BW utilization!
• Before compression
Router buffer
Overflows
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> DS3 TCP/IP performance enhancements
NetEx - HyperIP®
Orbital Data - IP Express
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< DS3 TCP/IP performance enhancements
Expand - IP Accelerators• 1800/4800/6800/9000 series
Peribit• SR20/50/55/80
Net Celera• T Series
River Bed - Steel Head • 500/1K/2K/3K/5K
Orbital Data• IP Express LC
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Caching appliancesRiver Bed - Steel Head 500/1K/2K/3K/5K
• CIFS & MAPI (NFS coming)
Tacit - Ishared Server
• CIFS & NFS
Kashya - KBX4000
• Includes volume replication, snapshot, & mirroring
• File & block replication
TCP/IP WAN
Appliance Appliance
Bi-directional
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Storage WAN for enterprise DR TCP enhancement caveats
Needs TCP enhancement
• Packet loss is an issue Long distance Big bandwidth Large amounts of
data Data migration Volume replication Snapshots High IOPS Bulk data transfers
May not need it
• Incremental data
• Only changed data
• Short time for net new data
• Asynchronous mirroring
• Short distance
• Small bandwidth
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Other issues to weigh
Shared WAN
Dedicated WAN
Shared cost & mgt.
• VLANs important
Dedicated cost & mgt.
• More flexibility
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Summary and conclusions
Build your DR foundation 1st
Calculate DR throughput requirements
Pick WAN technology of choice
If TCP determine need for enhancement
Implement
Reassess quarterly