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Go to SolutionSNAP VDEVs on disk?
Anyone have information on how SNAP VDEVs are created on disk? Is it on the SAVEDEV disks outside of the hyper slice area in the residual space? Is there a limit to the number of VDEVs that can be created? Any SNAP documentation exist that explains VDEVs in depth?
471
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Posted November 29th, 2007 12:00
I haven't seen the docs on this, but I know they are created on normal disk space (where the rest of your hypers are created). They are seperate from the SAVDEVS, but since they are created just like any other device too, they COULD reside on the same physical disk. Both types of devices are somewhat like "normal" devices, just with special attributes set on them. I have created both manually and the process is almost the same as creating standard devs.471
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Posted November 29th, 2007 13:00
Hopefully you would use most of the "normal" disk space with full size hypers. There would typically be some leftover space after the hyper slices are set (in the BIN) where the VDEVS are created. (VDEVs are tiny devices that emulate a full size hyper) In our case, we want the VDEVS on the same disks as our SAVEDEV disks.
Would you share your manual creation procedures for the SNAP devices?472
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Posted November 29th, 2007 14:00
the symconfigure script ?
create dev count=2, size=36828,emulation=FBA,config=VDEV;472
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Posted November 29th, 2007 19:00
Please note that SAV devices are normal or protected
disk hypers but are very slightly larger on physical
disk than their cylinder counts would indicate. This
is to cater for additional track pointer information
that needs to be preserved through IML and power
cycles. This slight size increase needs to be
considered if deleting non-SAV devices and creating
SAV devices with the same cylinder count instead.
MIchael,
does it mean that if you build save devices that you need to specify bigger size or DMX will automatically adjust save device size on the background ?
VDEV's are virtual devices but at 567x (DMX Family)
they require a Symmetrix Volume number, a full amount
of drive ID space & cache slots BUT with only a small
physical presence on disk. This small 2-MIR protected
physical presence on disk is again only track pointer
information (not track data) that needs to be
preserved through IML and power cycles.
what does it mean "full amount of drive ID space" Is it always 2-mir ..never Raid 5 ?472
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Posted November 29th, 2007 20:00
Hi Dynamox,
The SymmWin program will create the SAV devices with the number of usable cylinders specified in the SYMCLI command line. The size will automatically be increased on physical disk to cater for the required extra track pointers overhead.
You don't need to think about adjusting (reducing) the size=xxxx value unless the create command fails.
For example, I have seen clients delete 2-MIR BCVs of say 9206 cylinders and want to replace them with SAV & VDEV of the same cylinder size. The new SAV devices of size=9206 cylinders won't fit into the physical free space created by the previous online deletion. Since the SAV devices are part of a shared pool a smaller individual device size (say size=9200) is NO problem.
VDEVs require the same amount of "drive ID" space or physical cache overheads that the same cylinder count (AND full size on physical disk) STD volume would need (no free lunch).
VDEVs must be protected and are by default 2-MIR (not Raid-5). Note that the command file doesn't give you any options for seleting a protection method i.e. config=vdev.
Best Regards,
Michael.472
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Posted November 29th, 2007 20:00
VDEVs must be protected and are by default 2-MIR (not
Raid-5). Note that the command file doesn't give you
any options for seleting a protection method i.e.
config=vdev.
ok, so let's say i have DMX3 code 70. If i understand correctly code 70 does not allow different raid types on the same spindle. If my whole box is raid-5 (3+1) ...does it mean that i will not be able to create VDEV devices ? As usual ..thank you very much for taking the time to explain.472
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Posted November 29th, 2007 20:00
Hi Dynamox,
You're welcome (and I'm glad to know that someone finds my postings useful).
You can have 2-MIR and Raid-5 on the same spindles. This is not problem at any Enginuity level. I am not sure of the restriction that you are thinking of.....
Certainly from a performance and device management perspective you may want to restrict the volume placement (not mix 2-MIR & Raid-5 on the same spindles) but the SymmWin program won't stop you from doing so.
Regards,
Michael.472
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Posted November 30th, 2007 02:00
VDEVs require the same amount of "drive ID" space or
physical cache overheads that the same cylinder count
(AND full size on physical disk) STD volume would
need (no free lunch).
Michael could you please explain better what do you mean with "full size on physical disk" ?? How big is a VDEV on a drive ??
Thx :o)54
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Posted November 30th, 2007 08:00
Can you please clarify the statement:
"Note that at 577x (the DMX 3/4 Family) the VDEV is a genuinely cache only device (CDEV's) with NO presence on physical disk at all."
The last time I configured additional VDEVs ECC definately told me I was consuming a small amount of space on physical disk.
mlee2
108 Posts
472
0
Posted November 29th, 2007 19:00
Yes, that would be 100% correct. For example:
create dev count=2, size=18414, emulation=FBA, config=vdev;
create dev count=2, size=18414, emulation=FBA, config=2-way-mir, attribute=savedev;
The following may help when determining disk space requirements.
Please note that SAV devices are normal or protected disk hypers but are very slightly larger on physical disk than their cylinder counts would indicate. This is to cater for additional track pointer information that needs to be preserved through IML and power cycles. This slight size increase needs to be considered if deleting non-SAV devices and creating SAV devices with the same cylinder count instead.
VDEV's are virtual devices but at 567x (DMX Family) they require a Symmetrix Volume number, a full amount of drive ID space & cache slots BUT with only a small physical presence on disk. This small 2-MIR protected physical presence on disk is again only track pointer information (not track data) that needs to be preserved through IML and power cycles. Note that at 577x (the DMX 3/4 Family) the VDEV is a genuinely cache only device (CDEV's) with NO presence on physical disk at all.
I hope this helps.
Regards,
Michael.