Dynamic Spanned Disk, Hardware RAID, & Performance


I

IU-Dylan

Hello:

I would like to know what others have experienced, regarding performance of
dynamic spanned volumes, connected to an external hardware RAID enclosure.
My hardware RAID is RAID-5, comprised of eight (8) one terabyte (1 TB) hard
drives, in a single RAID array. Since this one array is larger than what XP
Pro (32-bit) can see, I have created four (4) two terabyte (2 TB) logical
unit numbers (LUNs), which correspond to four basic disks with XP Disk
Management. Since my client prefers to see only one (1) disk for the RAID
enclosure, I am considering creating a single dynamic spanned volume, which
will combine all four LUNs from the RAID array.

I assume there will be a performance hit. My questions are how much of a
performance hit will the PC suffer and what are others' experiences with
using dynamic spanned volumes, particularly dynamic spanned volumes linked to
a hardware RAID enclosure? Have others had problems with corruption or other
issues related to dynamic spanned volumes? What kind of performance hit have
others experienced in like scenarios and was it worth any benefits of the
configuration? If problems have occurred with dynamic volumes, how difficult
and/or possible was data restoration?

I know that dynamic volumes will limit access to only the later operating
systems and that Vista (both 32- and 64-bit versions) could see the single,
large basic volume, natively, as delivered by the external hardware RAID
enclosure, without a need to create four LUNs. However, my client and I are
quite hesitant to migrate to Vista, at this time. But, I am trying to weigh
the options of sticking with XP and using dynamic spanned volumes (on a
trusted and well-liked OS), verses using a newer, not-so-liked OS (Vista) and
having a native connection to a single basic volume from the RAID enclosure.

I would greatly appreciate everyone’s thoughts and comments. Thank you.

Sincerely,

--Dylan
 
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C

Carey Frisch [MVP]

This should open your eyes:

The Windows "Mojave Experiment"
http://www.mojaveexperiment.com/

Why RAID is (usually) a Terrible Idea
http://www.pugetsystems.com/articles?&id=29

RAID Explained
http://www.pugetsystems.com/articles.php?id=24


--
Carey Frisch
Microsoft MVP
Windows Desktop Experience -
Windows Vista Enthusiast

---------------------------------------------------------------

Hello:

I would like to know what others have experienced, regarding performance of
dynamic spanned volumes, connected to an external hardware RAID enclosure.
My hardware RAID is RAID-5, comprised of eight (8) one terabyte (1 TB) hard
drives, in a single RAID array. Since this one array is larger than what XP
Pro (32-bit) can see, I have created four (4) two terabyte (2 TB) logical
unit numbers (LUNs), which correspond to four basic disks with XP Disk
Management. Since my client prefers to see only one (1) disk for the RAID
enclosure, I am considering creating a single dynamic spanned volume, which
will combine all four LUNs from the RAID array.

I assume there will be a performance hit. My questions are how much of a
performance hit will the PC suffer and what are others' experiences with
using dynamic spanned volumes, particularly dynamic spanned volumes linked to
a hardware RAID enclosure? Have others had problems with corruption or other
issues related to dynamic spanned volumes? What kind of performance hit have
others experienced in like scenarios and was it worth any benefits of the
configuration? If problems have occurred with dynamic volumes, how difficult
and/or possible was data restoration?

I know that dynamic volumes will limit access to only the later operating
systems and that Vista (both 32- and 64-bit versions) could see the single,
large basic volume, natively, as delivered by the external hardware RAID
enclosure, without a need to create four LUNs. However, my client and I are
quite hesitant to migrate to Vista, at this time. But, I am trying to weigh
the options of sticking with XP and using dynamic spanned volumes (on a
trusted and well-liked OS), verses using a newer, not-so-liked OS (Vista) and
having a native connection to a single basic volume from the RAID enclosure.

I would greatly appreciate everyone’s thoughts and comments. Thank you.

Sincerely,

--Dylan
 
R

Richard

I am using RAID 1 in a Dell Dimension 8400 Computer with Windows XP SP3. How
can I tell if its a hardware or software controller?
 
I

IU-Dylan

Hello, again:

It appears that I might need to add a little clarification to my question.
I am already using and will continue to use an external hardware-based RAID
enclosure, using RAID-5, connected, via a SCSI HBA, to an XP Professional
high-end desktop machine. The raw storage capacity of the RAID enclosure is
nearly 8 TB, with RAID-5, my client will get about 6.6 TB of usable space.
Of course, the problem is that XP Pro (32-bit) can only see up to 2 TB on a
single partition or volume, since it does not support GPT partitions/volumes.
This would mean that I would have to create four separate LUNs within the
RAID enclosure, totaling approximately 2 TB each. With this configuration,
XP would see each LUN as a separate hard drive, which my client does not
want. The client wants only one "drive" to represent the entire RAID array
within the external RAID enclosure.

Therefore, considering the 2 TB limitation of XP Pro (32-bit) and my
client's wish to have only one "drive" representing the external RAID
enclosure, I am investigating the performance "hit" of creating four dynamic
volumes (from the four hard drives being presented from the external RAID
enclosure) and spanning all four into one dynamic, spanned volume, within XP
Pro. Therefore, the hardware-based RAID-5 enclosure would still be in play,
performing the RAID functions, while XP would only be conducting the OS host
virtualization of spanning the four external RAID-5 enclosure hard drives
into one dynamic spanned volume. This would present my client with one "hard
drive" within XP, representing the entire 6.6 TB external RAID array
enclosure. My concern is the performance hit the client may take on creating
such a configuration. Adaptec's website (Adaptec is the manufacturer of my
SCSI HBA) has some documentation on their website that states that such OS
host virtualization provides no performance penalty, which is somewhat
difficult for me to believe, which is why I am posing this question to the
newsgroup. I would like to know what others have experienced who may have
created like configurations.

Finally, the external RAID enclosure does provide an option to modify the
variable sector size of the array; however, while it does provide this
functionality, my understanding is that it is only there as a compatibility
feature, not as an enabling feature. In other words, when the external RAID
enclosure is connected to an OS that can natively see beyond the 2 TB limit
(XP Pro 64-bit, Vista 32- & 64-bit, Windows Server 2003 SP1, Windows Server
2008), this feature should be enabled. However, when connected to the older
OSs that cannot, natively, see beyond the 2 TB (XP Pro 32-bit, Windows 2000,
Windows NT 4, Windows ME, Windows 98/95, DOS), this feature should not be
enabled. I have tested this feature and while enabling this feature does
allow XP to see the entire 6.6 TB array, without creating a spanned dynamic
volume, it is quite unstable. Plus, Adaptec and Microsoft do not support
this type of configuration. This is why I am not using this particular
configuration and am considering the dynamic spanned volume. My concern is
that I have always stayed with basic disks and I wanted to understand any
performance hit that may be experienced by spanning these four LUNs from the
external hardware-based RAID array.

Once again, thank you to everyone who contributes.

--Dylan
 
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J

John John (MVP)

The two terabyte limit is a basic MBR disk limitation, not one of the
operating system, the partition table on MBR disk only supports
partitions to a maximum of two terabytes. Dynamic volumes are not
subject to this size limitation and thus can support much larger volume
sizes, as implemented, using the maximum 2^32 -1 4K clusters, Windows XP
supports dynamic volumes up to 16 terabytes.

John
 
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