1. 2
Disks and Things

2. Introduction This is a mix and match section
It contains all the information that does not have a home elsewhere in this presentation
It covers
Disk layouts
Disk Farms
Striping on Striping
April 28, 2019

3. Disk Layouts
In IQ (Simplex or Multiplex) the disk performance is critical to the overall speed of the system
In an IQ-M system you can have a number of different disk configurations
We consider the following
Simple SCSI (or UDMA-[1]66) Disks
Basic Disk “Farms” (Collections of raw disks)
RAID Systems (NT RAID, Clariion etc.)
Disk Subsystems (EMC, HDS[SunStor].)
April 28, 2019

4. Basic Disk Farms Here we are considering a number of “dumb” disks
There is no intelligence in the disks – or the controllers
Here is where we use IQ-M striping
Here we have a number of disk drives (on various controllers)
We stripe across a series of disks
April 28, 2019

5. Disk Striping Basic Disks 1-dimensional IQ Striping
In the 1-dimensional striping we are spreading the data writes (and reads) across a series of disk drives – limiting the overall disk head movement.
April 28, 2019

6. Problems with Disk Striping
IQ-M has to make location decisions as to where to write and read the data
It is not as simple as writing to “bit bucket” or a serial list of disk blocks
It is faster than simple 1 disk = 1 device
The performance hit is measured in extra micro seconds per read/write – but with a 10 TBytes database this could be important
April 28, 2019

7. RAID – 0,1 A D C B A D C B Redundant Array of Inexpensive Disks
In RAID 1 – Mirror, we can consider that Disks A and B are mirrored and Disks C and D
This improves read and write performance, as the controller will pick which disk heads are closer to the data required. Also there is an improvement in data security – 2 copies
Raid 1 - Mirror A D C B
In RAID 0 – Stripe, we can spread the reads and writes as per the last slide
Raid 0 - Stripe A D C B
This dramatically improves the read and write performance, but does nothing for the data security
April 28, 2019

8. RAID – 0/1 and 5 A D C B A D C B Redundant Array of Inexpensive Disks
In RAID 0/1 – Stripe and Mirror, we can see that the stripe sets on A and B mirror to C and D
This gives security – in the mirroring (copies) of the data, and improved performance due both to the two copies and the stripe sets
Raid 0/1 – Stripe and Mirror A D C B
In RAID 5 – Csum/MR, The data is in “stripes” across the disks then a checksum is written to the final disk
This gives a small performance improvement for reads, no improvement for writes (in fact it will slow writes down!). The only bonus is security. The system will allow a disk failure in the pack without requiring the 2 to 1 overhead of mirroring systems
Raid 5 – Checksum Multi-read A D C B
April 28, 2019

9. Other RAID There is RAID 2, 3 and 4
These are variations on the mirroring/striping and checksum theme
There are also proprietary RAID schemes
RAID S The is EMC’s RAID system
RAID M This is the MTI RAID Scheme
We will come on to talk about proprietary schemes in a few slides time
April 28, 2019

10. Well is RAID useful ? Yes it is – mainly !
If the RAID system handles the data distribution at the hardware level (with RAID controllers) then RAID is both fast and safe
Windows NT (and 2000) can drive RAID through the operating system
This can be slower than IQ-M performing the striping
Watch out for large numbers of reads – and individual read performance slowing down
RAID 5 on Disk Subsystems is a good compromise between speed and reliability
April 28, 2019

11. Disk Subsystems (emc, HDS)
These are disk arrays where we have no idea what the internal organization of the disks is (and nor do we care)
Generally we can consider that we are writing to memory (and usually we are!)
The tuning of the disks is usually best left up to the Hardware Support guys
April 28, 2019

12. Striping on Striping
There is one very contentious area in disk organisation
This is 2 dimensional disk striping or striping on stripes
This is driven by using an operating system or RAID unit to provide 1 dimensional striping on a series of disks
Then we apply IQ striping onto the existing striping
2 Dimensional stripes
Do it right – it’s very fast, do it wrong and it isn’t!
April 28, 2019

13. A diagram Operating System Striping AS IQ-M Striping
The reason this works is now the individual disks only have a very small amount of data to read and write so we rely on very fast disk -> processor communications
If this is done properly it is the fastest disk access for ASIQ-M
April 28, 2019

14. Disk Striping
By default Disk_Striping is set ON for RAW devices and OFF for file system devices
We should be using RAW devices – they are (generally) a lot faster and potentially safer than file system devices
You may want to play with this parameter if you are running devices on disk farms or RAID array systems
April 28, 2019

15. Disk Striping Packed
This was put in to the release – but is little used. This option changes the number of Allocation Maps from 1 to allowing each allocation map to present space in specific unit values, such as 1 Block, 2 blocks etc..
This allows for very slightly slower allocation of pages (minimal incremental cost), but better space utilization within the database – and in some case potentially faster allocation of space if there is a very fragmented store.
It is recommended that this is turned on at all times.
We will talk more about this during CREATE DATABASE
April 28, 2019

16. IQ Store Dbspace Management
New functionality permits removing a dbspace from the IQ Store
without interrupting database activity
You can add a new dbspace and move data from an 'old' disk to a new device
Drop a dbspace after all objects have been relocated
New Commands and Functions:
Determine database objects on a dbspace
Set a dbspace in 'read_only' status to prevent new writes
Move objects from one dbspace to another
April 28, 2019

17. IQ Store Dbspace Management
Dbspaces may be enlarged
For dbspaces created using 12.6, you may be able to enlarge a dbspace
In order to enlarge a dbspace you must 'reserve' space for the freelist when you create a new dbspace
Explanation follows
April 28, 2019

18. Sybase IQ Dbspace Basics
When you create a dbspace some pages are reserved for the 'freelist'
The freelist tracks pages that are available to hold data in that particular dbspace
The amount of space reserved for the freelist depends on the size of the dbspace
Freelist Pages
April 28, 2019

19. Reserving Space for the Freelist
New parameter in the Create Database and Create Dbspace commands allow for reserving space in the freelist
Command below creates a new dbspace reserving 5 MB for the freelist
Create dbspace newdbs as '/data/iqstore2' IQ STORE Size 500 Reserve 5
Freelist Pages
Reserved Pages
April 28, 2019

20. Alter Dbspace Command
With space for the freelist reserved you could increase the size of the dbspace using the Alter Dbspace command -
Alter dbspace newdbs
Size 750 MB
New Options for dbspace
READWRITE
READONLY
RELOCATE
April 28, 2019

21. Dbspace “Commands” sp_iqdbspaceinfo sp_dbspace sp_iqrelocate
What is located within the dbspaces
sp_dbspace
Usages and properties of the dbspace
sp_iqrelocate
Moves data between dbspaces
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22. Disk etc. - End
April 28, 2019