SAS and SAN questions.

Discussion in 'Mac OS X Server, Xserve, and Networking' started by mvmanolov, Feb 9, 2014.

  1. mvmanolov macrumors 6502a

    Aug 27, 2013
    Can someone point me in the direction of a good introductory reading into SAS and SAN and please don't say wikipedia... Thanks :d
  2. AmestrisXServe macrumors 6502

    Feb 6, 2014
    What kind of material are you after?

    Engineering & Design, to understand how the technology works?
    Implementation and Deployment?
    Usage and Administration?

    Do you want general, or OSX-specific literature?

    What is your present level of experience and expertise? (To avoid pointless subject matter that you already know.)
  3. mvmanolov thread starter macrumors 6502a

    Aug 27, 2013
    Thank you for this.

    i would say novice is my level of experience. i just read through some websites and got a general idea about how the tech works. So i am a little less interested in that. implementation and deployment i think i am most interested in, as well as usage and administration. Osx specific is what i need indeed.

    Again, thanks for taking the time.

    I like tinkering, and playing around with networking stuff, more a hobby than anything else, so i wanted to learn more about implementing either of theses at my home to mess about with.

  4. freejazz-man macrumors regular

    May 12, 2010
    Well, SAN's are pretty much on the way out as is SAS

    And what is wrong with wikipedia?
  5. ghellquist macrumors regular

    Aug 21, 2011
    Stockholm Sweden
    Storage Area Network

    There is no specific SAN support in OSX from start. You need to add the specific network card and the specific central server. As seen from OSX the SAN is simply normal discs where program and data are stored. Implementation, deployment and maintenance differs depending on what SAN solution you buy and is more or less tied to the actual central SAN server choosen.

    SAN is seldom used in "smaller" networks with only a few nodes. Here you would typically do a combination of local storage and NAS (discs on the normal network). OSX is, comparatively, seldom used as a server in larger data centers and hence will seldom use a SAN.

    A typical usage scenario in Windows Server or Linux data centers are that the servers are virtual. Meaning that there might be several virtual servers running on the same physical hardware box. There are several hardware boxes and the load can be moved between the boxes over time or when maintenance is required. One great advantage of having the storage on a SAN in that situation is that the load can easily be moved around -- a specific virtual server may be moved to a different hardware quickly without copying any discs.

    The central SAN server has a number of functions useable in a larger data center. One of the functions is flash backup -- making a backup seems to take a few seconds allowing very only very short stops in the service. (OSX has part of this functionality in the versioning file system).

    Maybe even, in some cases, the virtual server can be moved to the backup computer hall on the other side of the town while the application keeps on running. The virtual machine is made to "sleep" and moved to a disc image. The disc image is moved across the locations and the image is restarted at the new location. Some SAN-s allow realtime "mirroring" to a backup storage area, meaning that data is always available at two places even if one location goes "off-line", say because a fire.

    // Gunnar
  6. AmestrisXServe, Feb 12, 2014
    Last edited: Feb 12, 2014

    AmestrisXServe macrumors 6502

    Feb 6, 2014
    I have to agree here, that SAN and SAS literature, specific to OSX are pretty slim topics, as the implementation of SAN on the OSX platform was never popular.

    What i first suggest, is that you familiarise yourself with DAS SAS on OSX. There are only two major options to consider here:

    Is your SAS DAS array bootable, or not? If you do not need to boot from the array, you can use a variety of SAS cards, depending on your OS version. In my case, I use the Highpoint RocketRAID 2272 /alt/ Newertek miniSAS 6G-2e.

    What's the difference: In a word, firmware.

    The two products are Hardware Identical, but the HightPoint version has more current firmware, and supports accessory devices that you may find appealing. I have managed to use the EJ240 with both the HighPoint RR2722 and the Newertek 6g-2e, with some very minor driver hacking.

    Neither are bootable devices.
    If you want that, you enter a new level of cost (ATTO R644 PRICE), or work.

    The ATTO H608 and H644 ( and ESAS-R644-C00 respectively), and the ARC-1880ixl-8/12 ( are bootable SAS controllers, and may be good options if you need, or desire that feature.

    This last product supports EFI, has a wide RAID selection (lacking 15, 51 and 100) as follows: 1, 1E, 3, 5, 6, 10, 30, 50, 60, JBOD. For good storage array, DAS or SAN you are going to want RAID 10 or RAID 50. RAID-10 provies better data integrity via a fully mirrored stripe, whereas RAID-50 provides reasonable data integrity via parity and striping.

    These products will deliver multiple channels over a series of SAS ports, usually using the 8088 standard port spec for external, and 8086 spec for internal ports.


    Hacking it to Work

    There are also other solutions, that you may wish to view:

    Note that many of these require custom, modified or other kexts, and OS tinkering to get them to properly work. Following threads on forums dedicated to that is going to serve you better than any printed literature on the subject.

    If you want more information on hacking other cards to work, chat with me sometime in a separate thread on that subject. I do that kind of tinkering, as I run older OS versions and experiment to do a wide variety of bizarre stuff on OSX.

    I'm going to try to keep this thread very topical.


    SAS Literature

    The next thing you will want to do is read up on how SAS works.

    A pair of good refernece bopoks for you are:
    SAS Architecture (on Amazon)


    Mavericks Server Training Essentials

    There are 'Training Essentials' volumes from that same publisher covering OSX Server releases (back to at least 10.3), and a wider variety of topics. I keep the core trio for OSX Server 10.5 at hand at all times.


    1,024 Devices?

    Many sellers and manufacturers tout the '[128 devices'], failing to mention that to support 1,024 devices, you need 1,024 channels too.

    You're going to ask yourself? Do I need 1,024 ports, or what here?

    The short answer is: 'Yes and no.'

    Usually a single port on any SAS 4-channel card supports up top four devices on it, but you need a backplane to connect those devices to the interface. Most, but not all (warning, check first) enclosures have this kind of backplane. Enclosure selection is crucial if you want that full 1,024-devices.

    You see, some enclosures have backplanes that use a direct interface to connect one SAS 4-channel port to four drives (SAS or SATA), whereas others use SAS Expansion, which is what you will ultimately want.

    SAS expansion, you can look at as a form of multiplexing, although it is more complicated and actually provides additional channels to the host controller, however the host controller maximum throughput never changes.

    A pair of out of the box DAS solutions from Sonnet:

    You can always save money by building your own solution, starting with the interface, and then finding an enclosure. Enclosures with internal SAS expansion are sold constantly on eBay, and from recyclers. If you want NAS, you will have to ensure that your enclosure supports NAS, and if you want NAS and DAS via SAS, you will need to triple-check that data sheets.

    Here are two that has SAN and SAS DAS interfaces:

    Without some kind of expansion, you are limited to four devices per port (as each port has four channels).

    A chassis with SAS expansion will usually have one or two lanes of SAS-IN, with two lanes doubling the bandwidth to that enclosure; and a third lane of SAS-OUT, that you can use to daisy-chain it to another device.

    That means that you can connect another chassis--preferrably of the same kind--to your DAS and continue the chain.

    Some standalone devices may also be required in your array, and this is why you want multiple SAS ports on your host card. For example, my LTO drives have one SAS port, for one device. (Autoloaders and multi-drive tape arrays may use one port for more than one device.)

    That said, LTO support on OSX is terrible. There are only a few companies that offer LTO software, at a hideous price, whereas in Linux, you can do it with the OS directly. Why Apple didn't include LTO TAR support with their OS is beyond me. There is a very beta toolset called IOSCSITAPE that adds that functionality to OSX, but is 'Use at your own riskware'.

    Thankfully, if you do make a proper SAN, you could in theory use Linux to handle LTO operations.

    The other option, beyond daisychaining, is to use SAS Expanders, usually in the form of PCIe cards with more SAS ports, to add more channels. You can run these on any standard ATX mainboard, with or without a host OS.


    SAN & iSCSI

    A good literature starting point for you is Storage Networks Explained (on Amazon), as it covers DAS and NAS for ISCSI, SAS, Fibre Channel, InfiniBand, and FCoE (Fibre Channel over Ethernet).

    SAN support for OSX does exist. A products you will want to investigate is:

    This may work best with ATTO cards, and if you want to do SAN, you will want to look into iSCSI. Apple has their own Xsan technology as well.

    You will want SAN architecture devices, from the get-go, and you will want to read up on iSCSI in general.

    Here is the ATTO Apple page:

    Here is some more for you to read about iSCSI SAN on OSX:

    Note that most SAN stuff doesn't require SAS on your host, but will have an SAS expander in the SAN array device, connected via Ethernet to your Mac. This is why you should investigate SAN-specific devices, and software if you want to travel that road. DROBO is probably going to be your ideal choice for iSCSI on OSX.

    iSCSI is by design, system agnostic. it is an abstracted device (LUN), that may be formatted with a filesystem of its own by a host OS. You will likely want to use a filesystem that all of your hosts support, and you can get HFS+ filesystem (R/W) drivers for Windows and Linux, EXT filesystem drivers for Windows and OSX, and FAT-32 and NTSF drivers for OSX and Linux.

    Paragon, GmbH is a great company for this:

    If you operate your NAS with EXT, then you can use a Linux system to operate an LTO drive for backups. Keep in mind that whatever filesystem you use, if it does not support GUID, (i.e. if it uses MBR) you will need to hack OSX to boot from it.

    Whether you use MBR or GUID depends on what OS hosts you want to use. I have done this for multiboot systems, and you will want to read about Chameleon ( for more on that topic.


    Boot Volumes

    It is also important to realise that not all operating systems can boot from a NAS device, and few if any can use the iSCSI protocol to do so. You will need to attach them locally as DAS (in addition to their NAS capabilities) if you want to boot from them. (See:

    iSCSI can handle PXE stuff, you you can boot into some Linux environments over the NAS:

    Windows is going to be your troublemaker here, if your network is to consist of Windows nodes that you need to boot from the NAS.


    SAN or DAS?

    The main decision here is speed vs. abstraction. Do you want the full speed of DAS over SAS on a host system, or do you want the abstraction of one SAN over Ethernet; or do you want both?

    As far as I know, some devices support both SAN and DAS mounting, so you could have an enclosure mounted via a DAS connection over SAS, that also hosts as a SAN to other nodes on your network. You will need to do your homework and legwork to decide what is best for you, based on what is out there to buy, what you can afford, what your goal is for your network, and your ultimate needs vs. costs projection.


    Media Selection

    With any of these solutions, you will, at the end of the day have to make the call on what kinds of media to use. You have three primary choices: SAS, SATA, and FC drives. Each has their own pros and cons, and unless you really need a lot of speed performance, SATA will fit best into most applications.

    If you need a lot of speed for non-linear editing, rendering, and so forth, SAS and FC are the way to go, but cost a great deal more per GB than SATA. The bottom line is a comparison of cost, performance, and data capacity. Generally speaking, the higher the performance, the lower the data capacity in contrast to cost.

    I hope you find this helpful.


    P.S. I suggest printing, and making an offline archive of any website, forum post., etc, and a local copy of any software linked on any of the pages that relates to your project, putting them into an organised format, and making an archive of them (.gz or .zip, etc.) off-site, so that if any of the pages go down, or anyone takes their software (e.g. drivers, utilities) down, you can still access it later, as does not make whole-site copies. Tools such as Crawler for OSX are very useful in making a full mirror.

    Hard copy printing also ensures you have a printed reference on hand at all times. I have multiple binders filled with this kind of stuff, some of which has vanished forever from the Internet.
  7. AmestrisXServe macrumors 6502

    Feb 6, 2014
  8. mvmanolov thread starter macrumors 6502a

    Aug 27, 2013
    Thank you all, for these super informative and somewhat overwhelming replies. I think i'll take some time to take this all in, and buy some of the lit suggested here.


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