N&S Storage Foundations

  NAS and SAN Storage

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What is Centralized Storage?

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  • Storage Types
    • DAS – Direct Attached Storage
      • Computer has dedicated storage
      • Can be internal or external.
      • Storage does not have it’s own compute CPU, etc.
    • SAN – Storage Area Network
    • NAS – Network Attached Storage
      • Both provide centralized storage solutions for many computers
  • S & N Hardware
    • Very similar to a standard server
    • Mobo
    • CPU
    • Memory
    • NIC
    • Disks
    • Operating system
  • Smaller systems
    • Disks are generally enclosed in the same chassis
    • Will be built with redundancy
  • Large Storage systems
    • Redundant PS, controllers, etc.
  • Extra Large made by clustering together

The Benefits of SAN and NAS

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Disk Utilization with DAS

  • Requires massive over provisioning to plan for expected growth
  • Leave room for overhead.  Adding storage often requires downtime
  • Expect ~30% utilization
    • Massive wasted space over several servers
    • Costs very high

Using Centralized Storage

  • Storage systems use a centralized ‘pool’ of shared storage
  • Devices and applications can be allocated storage as required and easily changed on the fly, Non-disruptively
  • Centralized storage expect ~80% utilization across all servers.  Huge savings.

Thin Provisioning

  • Allows you to make it appear to the servers that they have more storage than you actually paid for
    • Purchased: 50 disks with 200GB = 10TB Total
    • Each server thinks is has 500GB
    • Over all, it looks like there is 25TB of disk, but you really only have 10TB
  • Use is split up, first come, first serve
  • Additional space can be added as needed, transparently to the servers

Deduplication and Compression

  • Deduplication detects and eliminates identical blocks
    • Eliminated blocks are replaced with a pointer to a single copy of the block on the disk
  • Compression detects and eliminates redundant data and white space in files.
  • Huge space savings are possible, dependent on the amount of duplicated blocks and compressible files.

Benefits

  • Pooled storage moves from “just in case” to “just in time” model for purchasing
  • Dedupe and compression provide additional space savings
  • This provides cost savings on hardware, rack space, power and cooling
  • Savings are multiplied as storage costs tends to come down over time.

Performance and Capacity

  • Access can be slower than DAS since network access can add latency BUT
  • Data can be striped across many disks
  • Storage vendors are also at the cutting edge of new storage technologies

Resiliency

  • SAN and SAS storage systems are always built to have very high degrees of resiliency
    • They almost always support mission critical systems
  • If a single component fails, there is a redundant component to take its place.

Centralized Management

  • Much easier to manage all your storage from a centralized location rather than separately across all your servers.

Diskless Servers

  • San protocols allow clients to boot up from a logical disk on the remote storage
  • Client servers do not need to contain any disks
  • Popular with blade servers

Storage Tiering

  • Storage systems can have medial with differing attributes, such as SSD and SATA (slower but higher capacity)
  • Frequently accessed (hot) data can be kept on SSD and ‘cold’ data can be archived onto the SATA drives

Centralized Backups

  • Traditional DAS: 50 servers = 50 backups
  • Centralized has centralized backups
    • Reduces backup windows
    • Does not required loading and unloading of physical media.

Snapshots

  • Point in time copy of the filesystem which can be used as a convenient short term backup
  • Consists of pointers to the original blocks on disk rather than being a new copy of the data, so they initially take up no space and occur nearly instantaneously.
    • This is NOT a separate copy!  If your storage system burns down, snapshots will also be destroyed.
  • If data gets corrupted or someone accidentally deletes a file, you can quickly recover from a snapshot
  • Good for quick and convenient backups and restores.
    • Still need real back ups.

Disaster Recovery

  • You can replicate data to a DR site
  • You can load balance incoming client requests for read-only data between different sites
    • You cannot do this with writable data since you need to maintain one consistent copy of the data.

Virtualization Support – vMotion

  • Software such as VMware and Hyper-V allow you to run multiple virutal servers on the same underlying physical hardware server
  • You can have a Linux Web server, Exchange mail server and SQL database servers all running on the same physical box, transparent to each of those virtual servers.
  • Killer feature of virtualization is the ability to move virtual servers between physical servers ON THE FLY while they are still running.
  • Virtual servers can keep on running with no outages even if the underlying physical server fails or is taken down for maintenance.
  • External storage is a requirement for this feature.

 

Storage Media Type

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RAID

 

Comparing SAN and NAS Storage

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