FAQ
Afternoon,

I've got an old Dell PERC 4DC (PCI 64bit/33MHz) sitting in my home rig
and with a new board on the way that has PCI-X (133) and PCIe (x4)
slots, I was wondering what people would recommend for a cheap
hardware parallel SCSI RAID controller (no fake raid please) that is
relatively cheap but faster then the old PERC? I'm looking for
something cheap that'll do RAID-10 but bonus points if it does
RAID-5/6. :-)


--
Drew

"Nothing in life is to be feared. It is only to be understood."
--Marie Curie

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  • John R Pierce at Apr 8, 2011 at 8:38 pm

    On 04/08/11 5:12 PM, Drew wrote:
    Afternoon,

    I've got an old Dell PERC 4DC (PCI 64bit/33MHz) sitting in my home rig
    and with a new board on the way that has PCI-X (133) and PCIe (x4)
    slots, I was wondering what people would recommend for a cheap
    hardware parallel SCSI RAID controller (no fake raid please) that is
    relatively cheap but faster then the old PERC? I'm looking for
    something cheap that'll do RAID-10 but bonus points if it does
    RAID-5/6. :-)

    cheap scsi raid? good luck. maybe something on ebay, but then its
    Caveat Emptor, and likely the raid batteries will be dead or dying.

    What speed is your scsi backplane? you can't get Ultra/320 speeds
    across older backplanes that were designed for U80 or U160 speeds. in
    fact, I've had a few backplanes that were supposed to be U320 but only
    worked reliably at U160 speeds, would get SCSI protocol errors when
    pushed under high IO loads at U320. 64bit 33Mhz PCI will sustain
    about 200MB/sec, which is about all you can get out of a single channel
    of U160 or slower SCSI anyways.
  • Drew at Apr 9, 2011 at 9:14 am

    cheap scsi raid? ?good luck. ? maybe something on ebay, but then its
    Caveat Emptor, and likely the raid batteries will be dead or dying.

    What speed is your scsi backplane? ?you can't get Ultra/320 speeds
    across older backplanes that were designed for U80 or U160 speeds. ?in
    fact, I've had a few backplanes that were supposed to be U320 but only
    worked reliably at U160 speeds, would get SCSI protocol errors when
    pushed under high IO loads at U320. ? ? 64bit 33Mhz PCI will sustain
    about 200MB/sec, which is about all you can get out of a single channel
    of U160 or slower SCSI anyways.
    In that case there's no real point upgrading. :-) The drives are U160's.

    I was just hoping a slightly newer card might be available that'd give
    me a speed boost for cheap. :-)


    --
    Drew

    "Nothing in life is to be feared. It is only to be understood."
    --Marie Curie
  • Christopher Chan at Apr 9, 2011 at 10:08 am

    On Saturday, April 09, 2011 09:14 PM, Drew wrote:
    cheap scsi raid? good luck. maybe something on ebay, but then its
    Caveat Emptor, and likely the raid batteries will be dead or dying.

    What speed is your scsi backplane? you can't get Ultra/320 speeds
    across older backplanes that were designed for U80 or U160 speeds. in
    fact, I've had a few backplanes that were supposed to be U320 but only
    worked reliably at U160 speeds, would get SCSI protocol errors when
    pushed under high IO loads at U320. 64bit 33Mhz PCI will sustain
    about 200MB/sec, which is about all you can get out of a single channel
    of U160 or slower SCSI anyways.
    In that case there's no real point upgrading. :-) The drives are U160's.
    The key is the backplane, not the drives. You should be able to get u320
    speeds if you have enough u160 drives.

    I was just hoping a slightly newer card might be available that'd give
    me a speed boost for cheap. :-)
    Again, like John posted, it depends on whether your backplane(s) can
    feed the u320 card and whether its bus can take the bandwidth.
  • Drew at Apr 9, 2011 at 10:47 am

    The key is the backplane, not the drives. You should be able to get u320
    speeds if you have enough u160 drives.
    Does five drives count?
    I was just hoping a slightly newer card might be available that'd give
    me a speed boost for cheap. :-)
    Again, like John posted, it depends on whether your backplane(s) can
    feed the u320 card and whether its bus can take the bandwidth.
    AFAIK, the back plane is rated at U320 speeds. The unit is a
    Supermicro CSE-M35S (SCA) which is listed as a U320 rated unit.


    --
    Drew

    "Nothing in life is to be feared. It is only to be understood."
    --Marie Curie
  • Christopher Chan at Apr 9, 2011 at 11:11 am

    On Saturday, April 09, 2011 10:47 PM, Drew wrote:
    The key is the backplane, not the drives. You should be able to get u320
    speeds if you have enough u160 drives.
    Does five drives count?
    I guess that depends on whether they can flood an u320 bus. If they are
    10k/15k rpm drives, I'd think so...
    I was just hoping a slightly newer card might be available that'd give
    me a speed boost for cheap. :-)
    Again, like John posted, it depends on whether your backplane(s) can
    feed the u320 card and whether its bus can take the bandwidth.
    AFAIK, the back plane is rated at U320 speeds. The unit is a
    Supermicro CSE-M35S (SCA) which is listed as a U320 rated unit.
    No experience with that particular unit but Supermicro has a good name.
    That would leave whether your mainboard's bus/slot can handle u320
    speeds or not if you do get a u320 card.

    Oh, another thing, if you are going to do raid5 or above, a big memory
    cache is king for the card. 64M of cache may or may not cut it. That
    Vortex with 1GB is definitely sufficient especially if it is BBU cache.
  • John R Pierce at Apr 9, 2011 at 4:30 pm

    On 04/09/11 8:11 AM, Christopher Chan wrote:
    On Saturday, April 09, 2011 10:47 PM, Drew wrote:
    The key is the backplane, not the drives. You should be able to get u320
    speeds if you have enough u160 drives.
    Does five drives count?
    I guess that depends on whether they can flood an u320 bus. If they are
    10k/15k rpm drives, I'd think so...

    Ummmm. say huh? if any one device on a SCSI channel is U160, the whole
    channel has to run no faster than U160, thats all she wrote. its a
    single bus not a 'star' like SAS or SATA.
  • Christopher Chan at Apr 10, 2011 at 6:09 am

    On Sunday, April 10, 2011 04:30 AM, John R Pierce wrote:
    On 04/09/11 8:11 AM, Christopher Chan wrote:
    On Saturday, April 09, 2011 10:47 PM, Drew wrote:
    The key is the backplane, not the drives. You should be able to get u320
    speeds if you have enough u160 drives.
    Does five drives count?
    I guess that depends on whether they can flood an u320 bus. If they are
    10k/15k rpm drives, I'd think so...

    Ummmm. say huh? if any one device on a SCSI channel is U160, the whole
    channel has to run no faster than U160, thats all she wrote. its a
    single bus not a 'star' like SAS or SATA.
    OH, is that how those babies work? The backplane is not using a
    controller chip that mutiplexes the stuff? Oops, sorry.
  • John R Pierce at Apr 10, 2011 at 6:37 am

    On 04/10/11 3:09 AM, Christopher Chan wrote:
    OH, is that how those babies work? The backplane is not using a
    controller chip that mutiplexes the stuff? Oops, sorry.

    The backplane typically has a SAF-TE
    (SCSI Accessed Fault-Tolerant Enclosure) chip which provides backplane
    management services, like notifying the raid controller or host software
    when devices are inserted or removed, as well as controlling device
    power, monitor enclosure environment, etc. In fact, SAF-TE itself is
    a SCSI device on the same backplane.


    Now, SAS backplanes do have multiplexers. One of the big functional[*]
    differences between SAS and SATA is that SATA only supports a simple
    expander where 1 SATA channel can be expanded to several devices,
    whereas a SAS multiplexor allows N SAS channels to talk to M devices. N
    is often 4, and M is usually the size of the drive tray. With the SATA
    version, if you had 4 SATA channels each exanded to 4 drives for 16
    drives total, drives 0-3 would always talk to SATA channel 0, drives 4-7
    to SATA 1, etc. with SAS, any channel can talk to any device, so you
    are less likely to run into bottlenecks



    [*] For the purpose of that description, I am ignoring the big
    implementation difference in that SAS uses SCSI commands to talk to
    drives, while SATA uses IDE/ATA derived commands. Another significant
    functional difference, SAS drives are commonly dual ported, so they can
    be connected to redundant host bus adapters or raid controllers, so if a
    controller fails, all devices are still addressable. SAS controllers
    are designed so they can talk to SATA drives, but SATA controllers can't
    talk to SAS devices.
  • Drew at Apr 9, 2011 at 11:12 pm

    I guess that depends on whether they can flood an u320 bus. If they are
    10k/15k rpm drives, I'd think so...
    10k rpm drives. I can also get my hands on some retired IBM U320's if
    I want to pull them from our shop's boneyard.
    No experience with that particular unit but Supermicro has a good name.
    That would leave whether your mainboard's bus/slot can handle u320
    speeds or not if you do get a u320 card.
    The X8SAX board I'm upgrading to uses a PCIe to PCI-X bridge chip to
    handle the two PCI-X slots. Based on my read of the manual, the x4
    link used on the PCIe side of the bridge is sufficient to drive a pair
    of PCI-X 133 slots at full capacity.


    --
    Drew

    "Nothing in life is to be feared. It is only to be understood."
    --Marie Curie
  • John R Pierce at Apr 9, 2011 at 4:28 pm

    On 04/09/11 7:08 AM, Christopher Chan wrote:
    In that case there's no real point upgrading. :-) The drives are U160's.
    The key is the backplane, not the drives. You should be able to get u320
    speeds if you have enough u160 drives
    SCSI (parallel) before U320 had a weak spot. the command and status
    phases of a SCSI command execution were stuck in asynch mode, only the
    data transfer phase could use synchronous ('fast', 'ultra', etc).
    Async SCSI is the old original 3-5Mhz mode, which on a wide bus means
    6-10MB/sec. This wasn't a big problem with the original Ultra Fast
    Wide 40 and Ultra 80 low voltage differential modes, but when SCSI hit
    U160 it became a potential bottleneck, especially for high rates of
    small block random IOPS on raids with more than a few drives.

    IIRC (rusty neurons), a SCSI command takes 16 bytes or so, and a status
    query takes 4-8. at the typical async 3Mxfer/sec, that means a command
    takes like 5 microseconds. In 5 microseconds at U160, you could have
    transferred 5*160 or 800 bytes, and a single status poll cycle takes
    another 16-200 bytes, or pretty much 1000 bytes total, eg, for every IO
    operation on the SCSI bus, you lose 1KB worth of potential data
    bandwidth... So if you're executing 1000 IOPS spread across 4-6 drives,
    you're losing at least 1MB/sec of your channel's bandwidth potential.
    in reality its several times worse than this due to the additional
    overhead of getting on the channel and the typical multiple polling
    cycles required to complete a transfer, I've calculated its as bad as
    10% under heavy IOPS random multiple drive raids

    U320 supports synchronous command and status, so its way more than
    double U160 speeds due to the elimination of this overhead.
    Interesting side note, U320 controllers and U320 devices can support
    synchronous command and status even if its running at U160 due to
    backplane and cable loading issues.

    thankfully, with FC, SAS, and SATA, these things are all history.
  • Kevin Thorpe at Apr 9, 2011 at 10:08 am
    I don't know where you are but I have a surplus ICP vortex proper Raid
    card with 1GB
    of cache - PCI-X. It was nearly ?1k when we bought it and it ran our
    main server for years.
    You're probably looking for a new one but someone can have this for
    beer money if it's
    of any use. I'm only going to have to pay to dispose of it (WEEE) anyway.
    On Sat, Apr 9, 2011 at 1:12 AM, Drew wrote:
    Afternoon,

    I've got an old Dell PERC 4DC (PCI 64bit/33MHz) sitting in my home rig
    and with a new board on the way that has PCI-X (133) and PCIe (x4)
    slots, I was wondering what people would recommend for a cheap
    hardware parallel SCSI RAID controller (no fake raid please) that is
    relatively cheap but faster then the old PERC? I'm looking for
    something cheap that'll do RAID-10 but bonus points if it does
    RAID-5/6. :-)


    --
    Drew

    "Nothing in life is to be feared. It is only to be understood."
    --Marie Curie
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