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This section contains some information and guidelines that
will help you plan your HP RAID 4Si configuration. To plan your configuration, follow these steps: Decide whether you
want to use the HP RAID 4Si controller as a boot device or as a
data device. Note that you can use
more than one controller as a boot device in a system. Consider the
dependencies for boot: Be sure
you have the correct PDC version. See the HP RAID 4Si Release
Note for information about the PDC versions. If you
do not have the correct PDC version, contact your Hewlett-Packard Support
representative. Although the HP RAID 4Si
controller has internal connections, you can connect it to only
external disks. If you want to use the controller
as a boot device, be sure it has HP RAID 4Si controller firmware
version U.01.04 or later. See “Downloading the Controller
Firmware” for more information. Be sure you have an alternate
boot device available (for example, a tape drive).
Keep in mind these special considerations: While
you are using a logical drive as a boot device (that is, while the
OS is running on it), you can use only View/Add Configuration, and
are limited in the configuration tasks you can do in IRM. This is
because IRM sees the logical drive as being in use, so any kind
of configuration changes affecting that drive are not allowed until
you are no longer using it as the boot device. Note that deleting
the last logical drive configured is also not allowed, even if the
drive you want to delete is not the logical drive being used as
the boot device. When you are no longer using
a logical drive as a boot device, if you clear the controller's
configuration—by doing either a New Configuration or a
Clear Configuration—that logical drive is deleted, too.
So, it is no longer set up as a boot device. If you want it to still
be a boot device, you must do the entire setup process again. If you have trouble accessing
your RAID boot data, only limited troubleshooting tools are available. IRM is the only tool you
can use to troubleshoot boot problems. So, you need to be able to
run it. You can run IRM in one of two ways: First way: If you
have an alternate boot media that has the HP RAID 4Si software installed
on it, boot from that media and then run IRM. (Note that we recommend having an alternate boot media—for
example, a disk that is not controlled by the HP RAID 4Si controller—with
the software on it.) Second way: You can run
Ignite-UX from the HP-UX 11.0 Core OS CD, the HP-UX 11i OE CD, or
the Ignite-UX server. IRM is one of the Ignite-UX options. (“Cannot Boot over RAID” describes the steps
for doing this.) When you use the SEArch command in the BCH menus to search for boot devices,
you get unusual results—the hardware path of the first
RAID logical drive on each controller is different from the other
logical drives. An example of the output from SEArch is shown below. Path# Device Path (dec) Device Path (mnem) Device Type
----- ----------------- ----------------- -----------
P0 0/0/2/0.6 intscsia.6 Random access media
P1 0/0/2/1.6 intscsib.6 Random access media
P2 0/8/0/1.0 Random access media
P3 0/8/0/1.0.0.1 Random access media
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In this example, P2 and P3 are both RAID logical drives. However,
the hardware path for P2 is slightly different, because it is the
first RAID logical drive on that controller. This is because any
extra zeros are removed in the search output. So, 0/8/0/1.0 is the same as 0/8/0/1.0.0.0, which is logical drive 0 at hardware path 0/8/0/1.0.0.0.
Choose the RAID level you want
to use for each logical drive. See the information from “Supported
RAID Levels” through “RAID
Level Decision Flow Chart”. Draw the physical disk configuration.
You should consider these things: You
might want to design one or more of your logical drives across controller
channels. This would protect against a cable disconnection and spread
the I/O load across the channels. If you want to use one or
more Hot Spares, keep in mind that it costs extra to do so. The
reason is that the Hot Spare's capacity is not available
unless the Hot Spare takes over for a failed disk. However, the
Hot Spare gives you extra protection in that a second disk failing will
not cause you to lose access to the disks in the logical drive.
To help you with your planning, you can use the worksheet
under “Physical
Drives”. Choose a stripe size. Keep in
mind that in most cases, 64KB and 128KB are the best stripe sizes,
and they generally will improve performance over the 8KB stripe
size. Use a smaller size only if you know your data will always
be written in smaller blocks. The default size is 64KB. (Note that
if you want to change the stripe size after data has been written
to the disks, you might have to save the data and then restore it
after you change the stripe size.) Determine the logical drive configuration
for the controller, considering these things: Only
logical drives can be accessed by HP-UX (physical drives are not).
Each logical drive is seen as a very large SCSI disk. The number of logical drives
you want to have. Remember that you can configure up to eight physical
disks in one logical drive. If you want to have more than eight
disks in a logical drive, you can use array spanning (see the next
bullet). When you do array
spanning, you associate logical drives with multiple
arrays (groups of physical disks). You can add the spanning to the
existing configuration or you can erase the existing configuration
and create a new spanned configuration. The RAID levels you can
configure using spanning are (1) RAID 1+0 (requires at least four
physical drives), (2) RAID 3+0 (requires at least six drives), and
5+0 (requires at least six drives). Do not put physical drives
of different capacities in the same logical drive. For example,
a JBOD can contain 9GB drives and 18GB drives, but do not put the
9GB drives and 18GB drives in the same logical
drive. HP-UX "sees" the
HP RAID 4Si logical drives as disks, so you can use the Logical
Volume Manager (LVM) to configure
them as physical volumes. Then, you can partition the drive into
separate logical volumes.
To help you with your planning, you can use the worksheet
under “Logical
Drives”. Determine these properties of
each logical drive: Write
Policy—Either write-thru (WRTHRU) or write-back (WRBACK). In WRTHRU mode, data is written to the cache and the disk.
In WRBACK mode, data is written to only the cache; it can
be flushed out to the disk from the cache. Note that WRBACK can increase performance significantly. So, we
recommend you specify
WRBACK unless the controller's battery health
is questionable—WRBACK relies on the battery to hold data in cache if
the HP-UX system loses power (a fully charged battery holds data
for up to 72 hours). So, if you use WRBACK, be sure the battery is in good condition (
irmd will tell you if it detects a problem with the
battery). The default is WRTHRU. Read Policy—
NORMAL, READAHEAD, or ADAPTIVE. NORMAL implies no read-aheads from disk are done.
READAHEAD means read ahead a full stripe from the disk.
ADAPTIVE implies read ahead a full stripe if two successive
READ calls are in the same stripe. ADAPTIVE provides the best performance, in most cases.
So, we recommend you use a different
setting only if you want to experiment to see if another setting
provides better performance. The default is ADAPTIVE. Cache Policy—Beginning
with HP RAID 4Si versions B.11.00.04 (HP-UX 11.0) and B.11.11.01
(HP-UX 11i), this is always set
to CachedIO, which means disk data is always cached in local
memory (that is, memory on the HP RAID 4Si controller). Note that
in earlier versions of HP RAID 4Si, Cache Policy could also be set
to DirectIO, which means that disk data (the requested amount)
is transferred directly to system memory. If you previously set
this to DirectIO (in an earlier version), and then installed one
of the above versions, this changes to CachedIO the first time you do a save of the configuration.
Decide whether you want to use
HP MirrorDisk/UX (product number B2491BA) to mirror across HP RAID
4Si controllers.
When you have completed all of these steps, you are ready
to start configuring your HP RAID 4Si controller. Go to the next
section, “Before
You Start Configuring”. |
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