Home > Articles > Networking

Storage in vSphere 5

This chapter is from the book

Disk Technology Considerations

This section examines a number of the factors to consider when deciding on the disk technology to use in your environment.

Supported Disk Types

As you have seen, storage architecture is important, and the disk technology plays an important part. ESXi supports a variety of disks, including SSD, SAS, FC, SATA, NL-SAS, IDE, USB, and SCSI.

Many options are available, making it possible to adapt the technology according to several criteria. As shown in Table 3.5, in terms of disk technology, many parameters are to be considered: speed expressed in revolutions per minute and in I/O per second (IOPS), as well as bandwidth transfers.

Table 3.5. Average Speed Parameters for Disk Types (May Vary)

Disks

RPM

IOPS

SSD

N/A

3000

SAS

15 K

180

SAS

10 K

130

NL-SAS

7.2 K

100

SATA

5.4

50

Solid-State Drives (SSDs) are high-performance drives composed of flash memory. These disks are nonmechanical. They are less likely to experience failures, they consume less energy, and they heat up much less than traditional disks. Their access time is low, with very high IOPS (3000 IOPS). They are ideal for reading but not well adapted to a large quantity of writes.

These disks are typically used for log files (for example, for databases). They are often used to extend the cache memory of controllers. (EMC calls them Fast Cache disks, and Netapp calls them Flash Cache disks.) In a VMware environment, these high-performance disks are ideal for storing the swap memory of VMs. They are also very useful for absorbing the charge when activity spikes appear—for example, in a VDI environment, when all VMs boot simultaneously. (This phenomenon is called a boot storm.) Disk sizes currently available are 100 GB, 200 GB, and 400 GB. Soon, 800 GB will also be available.

Serial Attached SCSI (SAS) disks replace Fibre Channel disks. These disks are directly connected to the controller, point to point. Revolution speeds are high—10,000 RPM or 15,000 RPM. They are ideal for applications with random access, and they can process small-size I/O of 8 bytes to 16 bytes, typically databases. The stream is bidirectional. Current disk sizes are 300 GB, 600 GB, and 900 GB.

Today, SAS disks are best adapted to virtual environments, and they offer the best price–performance ratio. Although FC disks are still widely found in production environments, the trend is to replace them with SAS disks.

Near-Line SAS (NL-SAS) disks use the mechanics of SATA disks mounted on SAS interfaces. Their advantage over SATA is that they transmit data in full duplex. Read and write can be performed simultaneously, contrary to SATA, which allows only a single read or write at a time. These disks offer features that allow the interpretation of SCSI commands, such as command queuing (to reduce read-head movements), and they provide better control of errors and reporting than SATA disks.

Serial-ATA (SATA) disks allow the management of a large capacity—2 TB, 3 TB, and soon 4 TB. They are recommended for the sequential transfer of large files (for example, backups, video files), but are not suitable for applications with elevated random I/O-like databases (for example, Oracle, Microsoft SQL, MySQL). They are unidirectional and allow a single read or write at a time. Depending on storage array manufacturers, SATA may or may not be recommended for critical-production VMs. Find out from the manufacturer. SATA disks are always well-suited for test VMs or for ISO image, template, or back-up storage.

RAID

Table 3.6 lists recommendations for RAID types and associated traditional uses.

Table 3.6. RAID Types and Traditional Uses

 

Write

Read

Use

Protection

RAID0

Excellent

Excellent

Real-time workstation

None (striping)

RAID1

Excellent

Excellent

DB log file, operating system, ESXi Hypervisor

Mirror

RAID5

Good

Very good

DB, ERP, web server, file server, mail

Parity

RAID6

Average

Very good

Archiving, backup, file server

Double parity

RAID10

Excellent

Excellent

Large DB , application servers

Striping + mirror

Storage Pools

In a physical environment, a LUN is dedicated to a server and, thus, to a specific application. In this case, parameters can be set to adapt RAID levels to the application, either sequential or random. This method is not well adapted to a virtual environment. Indeed, because of the dynamic nature of a virtual environment, keeping the same LUN-attribution logic based on the application becomes difficult. VMs are mobile and move from one datastore to another. RAID levels risk not remaining the same. Instead of using dedicated RAID levels, some manufacturers suggest using storage pools. This method is preferable because it offers excellent performance and simplifies management.

Automatic Disk Tiering

Only 20% of a LUN’s data is frequently accessed. Statistics also show that 80% of data is unused after two weeks. Through automatic tiering, frequently used data is automatically placed on high-performance SSD or SAS disks, while less frequently used data is stored on lower-performance disks such as SATA or NL-SAS.

Performance

In virtual environments, monitoring performance is complex because of resource pooling and the various layers (for example, applications, hypervisor, storage array). Speeds measured in IOPS and bandwidths in MBps depend on the type and number of disks on which the datastore is hosted. Storage activity should be monitored to determine whether waiting queues form on either of these criteria (queue length). At the hypervisor or vCenter level, the most reliable and simplest performance indicator for identifying contentions is the device access time.

Access time through all HBAs should be below 20 ms in read and write. Another indicator that should be monitored and that shows a contention by highlighting an activity that cannot be absorbed by the associated storage is the Stop Disk value. This value should always be set to 0. If its value is higher than 0, the load should be rebalanced. There are usually two causes:

  • VM activity is too high for the storage device.
  • Storage has not been properly configured. (For example, make sure there is no zoning issue, that all paths to storage are available, that the activity is well distributed among all paths, and that the storage cache is not set to forced flush.)

Additional Recommendations

Following are additional recommendations that can improve disk performance:

  • Using solid-state cache allows a significant number of I/O to disk. The cache serves as leverage because the major part of the read and write I/O activity occurs in the cache. Databases require very high I/O operations in 4-byte, 8-byte, or 16-byte random access, while video-file backup servers require high speeds with large block sizes (32, 64, 128, or 256 bytes).
  • Sequential access and random access should not be mixed on the same disk. If possible, I/Os should be separated by type (read, write, sequential, random). For example, three VMs hosting one transactional DBMS-type database should each have three datastores:
    • One datastore for the OS in RAID 5. Separating the OS means a VM can be booted without drawing from the database’s available I/Os from RAID 5.
    • One datastore for the RAID 5 database if the read/write ratio is 70%/30%. If not, the RAID type should be changed. A database generally uses 70% of random read-type transactions.
    • One datastore for logs in RAID 1 because writes are sequential (or RAID 10 for large databases with a high write rate).

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020