SAS vs. SATA Differences, Technology and Cost

Here are the high-level differences between SAS and SATA disk drives which I thought it’d be a perfect post for the blog as it contains some useful information that some might not be aware of.

Capacity:

  • SATA (or now called NL-SAS for Nearline SAS) disk drives are the largest on the market.  The largest SATA/NL-SAS drives available with widespread distribution today are 3TB.
  • SAS disk drives are typically smaller than SATA.  The largest SAS drives available with widespread distribution today are 600GB or 900GB.
  • So, for capacity, a SATA/NL-SAS disk drive is 4X-5x as dense for capacity than SAS.
  • A good way to quantify capacity comparison is $/GB.  SATA will have best $/GB.

Performance:

  • SATA/NL-SAS disk drives spin at 7.2k RPMs.  Average seek time on SATA/NL-SAS is 9.5msec.  Raw Disk IOPS (IOs per second) are 106.
  • SAS disk drives spin at 15k RPMs.  Average seek time on SAS is 3.5msec.  Raw Disk IOPS (IOs per second) are 294.
  • So, for performance, a SAS hard drive is nearly 3X as fast as SATA.
  • A good way to quantify performance comparison is $/IOP.  SAS will have best $/IOP.

Reliability: there are two reliability measures – MTBF and BER.

  • MTBF is mean time between failure.  MTBF is a statistical measure of drive reliability.
  • BER is Bit Error Rate.  BER is a measure of read error rates for disk drives.
  • SATA/NL-SAS drives have a MTBF of 1.2 million hours.  SAS drives have a MTBF of 1.6 million hours.  SAS drives are more reliable than SATA when looking at MTBF.
  • SATA drives have a BER of 1 read error in 10^15 bits read.  SAS drives have a BER of 1 read error in 10^16 bits read.  SAS drives are 10x more reliable for read errors.  Keep in mind a read error is data loss without other mechanisms (RAID or Network RAID) in place to recover the data.

Here are some good links for comparing disk types:
http://www.seagate.com/docs/pdf/datasheet/disc/ds_barracuda_es_2.pdf

http://www.seagate.com/docs/pdf/datasheet/disc/ds_cheetah_15k_7.pdf

http://h18004.www1.hp.com/products/servers/proliantstorage/drives-enclosures/index.html

http://storagebuddhist.wordpress.com/2011/07/01/nearline-sas-who-dares-wins/

http://www.seagate.com/docs/pdf/whitepaper/tp_sas_benefits_to_tier_2_storage.pdf

http://enterprise.media.seagate.com/2011/07/inside-it-storage/sas-mythbusters-data-highways-and-sas-vs-sata/

http://www.tomsitpro.com/articles/seagate-serial-attached-scsi-disk-drive-data-storage,2-119.html

http://en.wikipedia.org/wiki/Serial_attached_SCSI#Nearline_SAS

How To Collect Data From a Fibre Channel (FC) Switch

Sometimes you will be asked by either the manufacturers support or perhaps by Lewan for data from your Fibre Channel switch. Here is how you can gather that information in a format that helps support and/or Lewan:

Brocade – How-To Collect a “supportshow” from a Brocade Switch from a Windows Host with HyperTerminal
Follow these steps:

  1. Start the HyperTerminal program by selecting Start -> Programs -> Accessories -> Communications -> HyperTerminal.
  2. Make a new connection and select a name and icon for the connection.
  3. A “Connect to” window is displayed.
  4. Change the Connection using modem to TCP/IP (Winsock) and enter the IP address of the Brocade switch.
  5. Click the OK button.
  6. Log in to Brocade switch (default user: admin/default password: password), and then start to capture text. Select Transfer -> Capture text -> File C:supportshow.wri.
  7. Run the Brocade supportshow command.
  8. After the command completes, stop the “capture text” process (Transfer -> Capture text -> Stop).
  9. After completing this for all switches in all related fabrics, type quit and close the HyperTerminal session.

Cisco Support Logs

To capture support logs for a Cisco FC switch, following these instructions:

1) For firmware 1.2(x) and above telnet to the switch and open a capture session.
2) Run the following commands:
    term len 0
    show tech-support details
3) For firmware 1.0(4):  There is not a single command like a supportshow or data collection. There are two ways to get the outputs needed to troubleshoot most Cisco switch issues. Contact Lewan for additional information.

McDATA Switch Data Collection

In order to collect data from a McDATA switch being managed by McDATA’s EFCM utility, follow these instructions:

  1. Select the switch that you want to collect data from.
  2. Select Maintenance and then Data Collection.
  3. Enter a file name to call the file and then select save. Note the directory where the data is saved.  Once you select save, the data collection takes over and the files is downloaded to the local PC and stored in the directory specified.

How to collect switch information and related data from a McDATA DS-16M, DS-32M or another switch with EWS:

These switches (also known as ES3016 and ES3032)  have an Embedded Web Server (EWS) GUI. You can access this through a web browser by entering the IP Address in the URL address line  (that is, http:/10.14.1.92).  Once you have logged in you can run a script that collects switch information including: Network Info, Operating Parameters, Zone Info, Port Login Data, Port Data and Port Types, and Switch Status.

Note:  These model switches do not support serial port connectivity for information retrieval.

To collect this information, follow these steps:

  1. Once you have logged in to the EWS GUI, click on ” Operations ” from the left frame of the EWS GUI.
  2. Click the third tab called “Maintenance.”
  3. Click the secondary tab labeled Product Info.
  4. Click Product Information. This will generate a report.
  5. Click “File” on the web browser toolbar and select “Save As” to save the .txt file with either the default name or one that you rename it to. Save it on the desktop or to a directory where you can locate it so that you can email it to Technical Support.

To locate the switch firmware revision, follow these steps:

  1. Click “View” from the left frame of the EWS GUI.
  2. Select Unit Properties. The last entry of that page has the firmware level.

Forget Dropbox – Use Zumodrive for Online Storage!

I posted awhile back about DropBox which allows you to store things online while having a local “drive” on your computer to use. Here’s a link to that post:
http://djlaube.wordpress.com/2009/02/18/dropbox-online-sync-backup-for-multiple-computers/

Well, forget Dropbox! Nothing against them as it worked well, however I now use www.zumodrive.com! It basically has all the features of Dropbox (creates a “local drive” on your PC, can use for backup, keeps a local copy if you want it to, etc) and works great on my Mac, but I’ve also installed on a Windows PC and synced files between the two without any problems. The sync seems very intelligent and “just works”. I also like how you can share files out to anyone by creating a link you can email. You can also share files to other ZumoDrive users, without it affecting their space under their account (unlike DropBox where sharing affects both users space) which is great if you have to work on a project or something with someone, but you don’t need to give them your ZumoDrive login.. just create their own account and share what you want with them.

Hope it helps!

Celerra Virtual Storage Appliance (VSA) for VMware

I have used the Lefthand Networks Virtual Storage Appliance (VSA) in the past (which can be found here: http://www.lefthandnetworks.com/vsa.aspx) which presents an iSCSI target off of local disk through an appliance inside a VM. It’s a great way to use internal storage and make it “look” and act like a SAN.

I ran across this How-To for EMC’s Celerra VSA, which I didn’t really know about. So here’s the link to the How-To:
http://virtualgeek.typepad.com/virtual_geek/2008/08/celerra-virtual.html