One of the resources at HP (thanks Ben!) made the following comment to one of our customers and I thought it’d be a perfect post for the blog as it contains some useful information that some might not be aware of.
Here are the high-level differences between SAS and SATA disk drives:
- 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.
- 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:
Here’s some RAW SAN network speeds that I found in some post somewhere (which I didn’t write down).. Obviously there are a lot of caveats related to this, but from a pure bandwidth perspective, I thought this was interesting for reference.
1 gig = 125 MB/sec
2 gig = 250 MB/sec
4 gig = 500 MB/sec
8 gig = 1000 MB/sec
10 gig = 1250 MB/sec
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:
- Start the HyperTerminal program by selecting Start -> Programs -> Accessories -> Communications -> HyperTerminal.
- Make a new connection and select a name and icon for the connection.
- A “Connect to” window is displayed.
- Change the Connection using modem to TCP/IP (Winsock) and enter the IP address of the Brocade switch.
- Click the OK button.
- 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.
- Run the Brocade supportshow command.
- After the command completes, stop the “capture text” process (Transfer -> Capture text -> Stop).
- 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:
- Select the switch that you want to collect data from.
- Select Maintenance and then Data Collection.
- 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:
- Once you have logged in to the EWS GUI, click on ” Operations ” from the left frame of the EWS GUI.
- Click the third tab called “Maintenance.”
- Click the secondary tab labeled Product Info.
- Click Product Information. This will generate a report.
- 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:
- Click “View” from the left frame of the EWS GUI.
- Select Unit Properties. The last entry of that page has the firmware level.
On my to-do list was to write up a How-To on using OpenFiler iSCSI storage appliance with VMware ESX. The OpenFiler appliance is a free appliance that you can use to turn local storage into an iSCSI target. Well, Simon over at TechHead in the UK did a bang up job (that’s London speak!) with a How-To detailing installing the OpenFiler software and using it with ESX.
I’ve heard great things about OpenFiler from our customers who are using it. Keep in mind, you’ll want to keep OpenFiler in DR environments or Test/Dev environments as there is some limits on performance. But those who are looking for a free iSCSI target or appliance, it’s a good one.
You might also check out our other post on some of the other common iSCSI appliances, very similar to OpenFiler:
VM/ETC posted awhile back an excellent article about a free iSCSI SAN VM appliance that you can download from Xtravirt, which I just found today. It doesn’t sound like it can scale beyond using storage from 2 ESX servers, but for a really small environment or a home lab, it might do the trick.
This post is similar to these other options we’ve mentioned for iSCSI SAN VM appliances:
I found this really useful program called DropBox. It’s another Beta program that’s taking a “cloud” approach to storing files and data. It looks to be for home/SMB use but I’ve found it very useful so far. You can use it on Mac, Windows or Linux and store your files online and sync all of the files between computers (for those Mac users out there, think .Mac or MobileMe functionality, without the Apple pricetag). It also does versioning (for backup sake), as well as un-delete and all that jazz. You can also share files with users by giving them a direct link to folders or files, say for a team project or something.
Hope it’s useful to you!
Most organizations believe that their data is well protected because they have a backup system in place, or because they use a RAID array to protect their data against disk failure. The truth is very few entities have complete protection.
A complete data protection solution requires protection in several areas. Hardware resiliency protects against component failure. Point in time protection ensures that data can be recovered from some point in the past, whether seconds, minutes, hours or days. Geographic protection prevents loss of data in case of some sort of site wide failure. Many organizations also require some sort of long term retention of critical data for compliance purposes or in case of legal action.
The following list describes some of the strategies used for each type of data protection:
Hardware Resilience – Protects against hardware component failure:
RAID Controller cards
External Storage Arrays
Point-in-time Protection – Protects against data loss or corruption due to hardware or software failure, user error or deliberate actions:
Enterprise Backup Utilities
Software or Hardware Based Snapshots
Continuous Data Protection Tools
Geographic Protection – Protects against site wide failures:
Off-site Tape Storage
Disk based backup replication
Storage Array Based Replication
Long-Term Protection – Used when business or legal policies require retention of data beyond standard backup retention:
File System and E-Mail Archiving