Storage Technology and Management

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Storage Technology and Management

• W.lilakiatsakun

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Storage Technology

• JBOD (Just Bunch Of Disk)
• RAID (Redundant arrays of inexpensive disks)
• SSA (Serial Storage Architecture)

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JBOD (Just Bunch Of Disk) (1)
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JBOD (Just Bunch Of Disk) (2)

• JBOD can be used as individual disks or any RAID
  configuration or Concatenation (SPAN) depending
  on the Host Bus Adapter
• Concatenation or Spanning of disks is a popular
  method for combining multiple physical disk
  drives into a single virtual disk.
• It provides no data redundancy.
• Disks are merely concatenated together so they
  appear to be a single large disk.

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JBOD (Just Bunch Of Disk) (3)

• For example, JBOD (Just a Bunch Of Disks) could
  combine 3 GB, 15 GB, 5.5 GB, and 12 GB drives
  into a logical drive at 35.5 GB, which is often
  more useful than the individual drives separately.

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Redundant arrays of inexpensive disks (RAID)

• The organization distributes the data across
  multiple smaller disks, offering protection
  from a crash that could wipe out all data on a
  single, shared disk.
• Benefits are depended on level of RAID

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RAID0 (stripe set or striped volume)

• RAID Level 0 splits data evenly across two or
  more disks (striped) with no parity information
  for redundancy.
• It is important to note that RAID 0 provides zero
  data redundancy.
• RAID 0 is normally used to increase performance
• A RAID0 can be created with disks of differing
  sizes, but the storage space added to the array
  by each disk is limited to the size of the
  smallest disk

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RAID0 Summary (1)

• RAID 0 uses a very simple design and is easy to
  implement with a HUGE performance advantage.
• I/O performance is greatly improved by spreading
  the I/O load across many channels and drives
  while the best performance is achieved when data
  is striped across multiple controllers with only
  one drive per controller.

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RAID0 Summary (2)

• No parity calculation overhead is involved
• Not a "True" RAID because it is NOT
  fault-tolerant.
• The failure of just one drive will result in all
  data in an array being lost.

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RAID1 (mirrorring)

• A RAID 1 creates an exact copy of a set of data
  on two or more disks.
• This is useful when read performance or
  reliability are more important than data storage
  capacity.
• Such an array can only be as big as the smallest
  member disk.
• A classic RAID 1 mirrored pair contains two disks
  which increases reliability

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RAID1 Summary (1)

• RAID Level 1 requires a minimum of 2 drives to
  implement.
• 100 redundancy of data means no rebuild is
  necessary in case of a disk failure, just a copy
  to the replacement disk.
• Transfer rate per block is equal to that of a
  single disk.
• Simplest RAID storage subsystem design.

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RAID1 Summary (2)

• Highest disk overhead of all RAID types -
  inefficient due to the duplication of Write
  tasks.
• Typically the RAID function is done by system
  software, loading the CPU/Server and possibly
  degrading throughput at high activity levels.
• Hardware implementation is strongly recommended.
• May not support hot swap of failed disk when
  implemented in "software".

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RAID 0 1 (A Mirror of Stripes)

• RAID Level 01 is implemented as a mirrored array
  whose segments are RAID 0 arrays.
• RAID Level 01 requires a minimum of 4 drives to
  implement

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RAID 10 (A Stripe of Mirrors)

• RAID 10 is implemented as a striped array whose
  segments are RAID 1 arrays.
• RAID Level 10 requires a minimum of 4 drives to
  implement.

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RAID3 (Parallel access with a dedicated parity
disk)

• RAID Level 3uses byte-level striping with a
  dedicated parity disk.
• This comes about because any single block of data
  will be spread across all members of the set and
  will reside in the same location.
• So, any I/O operation requires activity on every
  disk.

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RAID3 Summary

• Level 3 only requires one dedicated disk in the
  array to hold parity information.
• The server's data is then striped across the
  remaining drives, usually one byte at a time.
• The parity drive then keeps track of all the info
  on the striped drive(s) and uses it to restore
  info if the drive should fail.
• Because of the parity information that is stored
  and because Write operations take place on a byte
  level, Read/Write operations often take longer
  than other RAID configurations.

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RAID5 (Independent access with distributed parity)

• A RAID 5 uses block-level striping with parity
  data distributed across all member disks.
• A minimum of 3 disks is generally required for a
  complete RAID 5 configuration.
• In the example, a read request for block "A1"
  would be serviced by disk 0.
• A simultaneous read request for block B1 would
  have to wait, but a read request for B2 could be
  serviced concurrently by disk 1

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RAID 5 Summary

• Level 5 also relies on parity information to
  provide redundancy and fault tolerance using
  independent data disks with distributed parity
  blocks.
• Each entire data block is written onto a data
  disk parity for blocks in the same rank is
  generated on Writes, recorded in a distributed
  location and checked on Reads. Compared to RAID
  3, RAID 5 uses striping to spread parity
  information across multiple drives.
• Requirements RAID Level 5 requires a minimum of
  3 drives to implement.

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SSA (Serial Storage Architecture) (1)

• Serial Storage Architecture (SSA) defines a
  high-performance serial link for the attachment
  of input/output devices.
• It has been optimized for storage applications
  such as hard disk drives, host adapter cards, and
  array controllers.
• SSA has many advantages over existing parallel
  interfaces such as the Small Computer Systems
  Interface (SCSI-2).
• It uses compact cables and connectors, and it has
  better performance, connectivity, and
  reliability.

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SSA (Serial Storage Architecture) (2)

• Disk Subsystem provide a peak data rate of 20
  MB/s in each direction.
• However, a typical loop configuration with one
  host adapter can provide a total sustained
  bandwidth of up to 80 MB/s, and higher speeds are
  becoming available.
• The physical medium is usually a copper cable up
  to 20 meters long, but fiber optics can also be
  used for longer distances.

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SSA (Serial Storage Architecture) (3)
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SSA (Serial Storage Architecture) (4)

• Architecture overview
• SSA is defined in three layers
• SSA-PH1 defines the electrical specifications,
  cables, and connectors.
• SSA-TL1 is a general-purpose transport layer. It
  defines the transmission protocol, configuration,
  and error recovery.
• SSA-S2P is a mapping of the SCSI-2 queuing
  model, command set, status, and sense bytes.

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Storage Model
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Storage Area Network

• A SAN is a specialized, high-speed network
  attaching servers and storage devices
• It is sometimes referred to as the network
  behind the servers.
• A SAN introduces the flexibility of networking to
  enable one server or many heterogeneous servers
  to share a common storage utility, which may
  comprise many storage devices, including disk,
  tape, and optical storage.

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SAN Component

• SAN Connectivity
• the connectivity of storage and server components
  typically using Fibre Channel (FC).
• SAN Storage
• TAPE /RAID /JBOD (Just Bunch of Disk) /SSA
  (Serial Storage Architecture)
• SAN Server
• Windows /Unix /Linux and etc

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Switched Fabric

• An infrastructure specially designed to handle
  storage communications called a fabric.
• A typical Fibre Channel SAN fabric is made up of
  a number of Fibre Channel switches.
• Today, all major SAN equipment vendors also offer
  some form of Fibre Channel routing solution, and
  these bring substantial scalability benefits to
  the SAN architecture by allowing data to cross
  between different fabrics without merging them.

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Fiber Channel protocol (1)

• FC0 The physical layer, which includes cables,
  fiber optics, connectors, pinouts etc.
• FC1 The data link layer, which implements the
  8b/10b encoding and decoding of signals.
• FC2 The network layer, defined by the
• FC-PI-2 standard, consists of the core of Fibre
  Channel, and defines the main protocols.

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Fiber Channel protocol (2)

• FC3 The common services layer, a thin layer that
  could eventually implement functions like
  encryption or RAID.
• FC4 The Protocol Mapping layer. Layer in which
  other protocols, such as SCSI, are encapsulated
  into an information unit for delivery to FC2.

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Storage Management

• Monitoring disk use
• Disk monitor agent scans the server volumes to
  collect disk use information
• Hierarchical storage management
• Files will be archived according to certain
  criteria
• Prevention against Data Loss
• To protect and recovery from loss
• Outsourcing storage management

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Monitoring disk use

• One or more the following categories of
  information can be collected
• Volumes(Disk) total space used /available
• Directories what are there
• Directory and File owners who create / who use
  /when create

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Hierarchical storage management

• When disk space becomes exhausted , data files
  need to be backup (as archived file or back up
  tape)
• Software tools (Back up tools)
• When a file system reaches a predefined threshold
  of X percent full
• automated procedure are initiated that determine
  which files are eligible for archive and are
  currently backed up
• The file catalog is then updated to indicate that
  files have been archived and deletes them from
  the disk file system

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Prevention against data loss (1/2)

• Data perspective
• Backups sent off-site in regular intervals
• Use a Remote backup facility if possible to
  minimize data loss
• Storage Area Networks (SANs) over multiple sites
  make data immediately available without the need
  to recover or synchronize it

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Prevention against data loss (2/2)

• Facility perspective
• Surge Protectors to minimize the effect of
  power surges on delicate electronic equipment
• Uninterruptible Power Supply (UPS) and/or Backup
  Generator
• Fire Preventions more alarms, accessible
  extinguishers
• Anti-virus software and other security measures

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Techniques to prevent data loss

• Mirroring
• Disk mirroring Redundant arrays of inexpensive
  disks 1 (RAID1)
• Server mirroring web / ftp /email
• On-site data storage
• Back up - Tape / optical disk
• Off-site data storage (backup-site)
• Cold sites
• Warm sites
• Hot site

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Mirroring

• Mirroring can occur locally or remotely.
• Locally means that a server has a second hard
  drive that stores data.
• A remote mirror means that a remote server
  contains an exact duplicate of the data.
• Data is written to the original drive when a
  write request is issued and then copied to the
  mirrored drive, providing a mirror image of the
  primary drive.

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Disk mirroring (RAID1)

• The replication of logical disk volumes onto
  separate physical hard disks in real time to
  ensure continuous availability, currency and
  accuracy.
• A mirrored volume is a complete logical
  representation of separate volume copies

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Server mirroring

• Mirror sites are most commonly used to provide
  multiple sources of the same information, and are
  of particular value as a way of providing
  reliable access to large downloads.
• Web server
• To preserve a website or page, especially when it
  is closed or is about to be closed
• Load balancing
• Email server
• To protect loss of email information
• ftp server
• To allow faster downloads for users at a specific
  geographical location
• Load balancing

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Back up site

• A backup site is a location where a business can
  easily relocate following a disaster, such as
  fire, flood, or terrorist threat. This is an
  integral part of the disaster recovery plan of a
  business.
• A backup site can be another location operated by
  the business, or contracted via a company that
  specializes in disaster recovery services.
• In some cases, a business will have an agreement
  with a second business to operate a joint
  disaster recovery facility.

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Cold Sites

• A cold site is the most inexpensive type of
  backup site for a business to operate.
• It provides office spaces to operate
• It does not include backed up copies of data and
  information from the original location of the
  business, nor does it include hardware already
  set up.
• The lack of hardware contributes to the minimal
  startup costs of the cold site, but requires
  additional time following the disaster to have
  the operation running at a capacity close to that
  prior to the disaster.

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Warm Sites

• A warm site is a location where the business can
  relocate to after the disaster that is already
  stocked with computer hardware similar to that of
  the original site, but does not contain backed up
  copies of data and information.

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Hot Sites

• A hot site is a duplicate of the original site of
  the business, with full computer systems as well
  as near-complete backups of user data.
• Ideally, a hot site will be up and running within
  a matter of hours. This type of backup site is
  the most expensive to operate.
• Hot sites are popular with stock exchanges and
  other financial institutions who may need to
  evacuate due to potential bomb threats and must
  resume normal operations as soon as possible.

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How to choose (1)

• Choosing the type is mainly decided by a
  company's cost vs. benefit strategy.
• Hot sites are traditionally more expensive than
  cold sites since much of the equipment the
  company needs has already been purchased and thus
  the operational costs are higher.
• However if the same company loses a substantial
  amount of revenue for each day they are inactive
  then it may be worth the cost.

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How to choose (2)

• The advantages of a cold site are simple--cost.
  It requires much fewer resources to operate a
  cold site because no equipment has been bought
  prior to the disaster.
• The downside with a cold site is the potential
  cost that must be incurred in order to make the
  cold site effective.
• The costs of purchasing equipment on very short
  notice may be higher and the disaster may make
  the equipment difficult to obtain.