DJDishwateR
Gawd
- Joined
- Jul 12, 2003
- Messages
- 633
I know there's the spare drive for RAID 5, but is there any formula to figure out how much storage space is lost after creating the array?
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RAID 5 overhead
- Thread starter DJDishwateR
- Start date
D
Deleted member 68403
Guest
Originally posted by Anarchy
Ice Szar will soon post a link that explains RAID5 better than i have
Ice Czar will learn you well. Very well.
I
Ice Czar
Guest
thats it, efficiency increases with the number of drives
3 x 20GB = 40GB
4 x 20GB = 60GB
5 x 20GB = 80GB
6 x 20GB = 100GB
7 x 20GB = 120GB
8 x 20GB = 140GB
9 x 20GB = 160GB
10 x 20GB = 180GB
11 x 20GB = 200GB
12 x 20GB = 220GB (3ware makes a 12 channel IDE RAID card)
x 10 for 200GB HDDs
2.2TB\2200GBRAID 5
Technique(s) Used: Block-level striping with distributed parity.
Hard Disk Requirements: Minimum of three standard hard disks; maximum set by controller. Should be of identical size and type.
Array Capacity: (Size of Smallest Drive) * (Number of Drives - 1).
Storage Efficiency: If all drives are the same size, ( (Number of Drives - 1) / Number of Drives).
Fault Tolerance: Good. Can tolerate loss of one drive.
Availability: Good to very good. Hot sparing and automatic rebuild are usually featured on hardware RAID controllers supporting RAID 5 (software RAID 5 will require down-time).
Degradation and Rebuilding: Due to distributed parity, degradation can be substantial after a failure and during rebuilding
Ive been runing a 6 channel Promise SX6000 w\ 128MB PC133 cache for over 2 years
6 x 40GB WD400BB for usable array of 200GB (186.26 Binary w\ NTFS overhead)
DJDishwateR
Gawd
- Joined
- Jul 12, 2003
- Messages
- 633
I knew the basics of RAID 5 ice czar thanks anyways, someone told me there was overhead for the parity, but it ended up being a confusion of what each of us were saying, thanks anyways. Whats the best stripe size for purely performance on some 160 GB EIDE HD's?
I
Ice Czar
Guest
the overhead greatly varies with the controller employed
my XS6000 has a dedicated RISC processor just for XOR calculations and it doesnt impact my CPU much if at all, on the otherhand if its software RAID 5 it can be quite alot, (so much so that you might consider a Linux RAID5 which I here is more effecient, cnat confirm)
regarding stripe size, youd typically try to match to your access
so if your dealing with large files (video graphics ect) you employ larger stripes, if its lots of small access then smaller stripes, benchmarks are almost universally biased to the smaller stripes.
Im just going to cut and paste another thread here
-------------------------------------------------------------------
1.) How would I determine the best stripe size? I heard you can choose between good write performance on a sliding scale depending on the stripe size. If possible, id like a balance between the two like below.
Read ----------|---------- Write
Stripe Size
the read vs write balance isnt controlled by the stripe size per se, that involves caches, the controller, the size of the access, and the stripe.
2.) How does the stripe size relate to the cluster size?
same link as above
3.) FAT32's file size limit is 4GB, if I had 2 drives on RAID 0, would the max filesize be 8GB (is it 4GB limit per disk or 4GB limit overall?)
No, the OS see the array as a single HDD, and its a filesystem limit anyway (you should be using NTFS without some other truely compelling reason anyway.)
4.) How do you go on about formatting, partitioning and defragging a RAID 0 set? Is it just the same as you would with 1 drive?
Yes, however making an array bootable is more complex, typically you have to set it bootable in the RAID's BIOS and when installing the OS you will be prompted to load additional SCSI drivers by pressing F6, and then you load the RAID driver (which is SCSI)
5.) I think the defauly cluster size for NTFS in XP Home is 4kb, would the stripe size be best as a multiple of 4?
The default cluster size is dependent on the size of the partition you can manually set a cluster size when you partition
6.) If the cluster size if 4kb and the stripe was set to 2kb for example, would I waste a ton of space? (I noticed that smaller cluster size is more efficient storage, probably because of part filled clusters)
refer to above
7.) Is RAID really unreliable? I hear a few stories that put me off a bit, but it's something I want to try for myself.
Small problems can become big, the potential to loose data more than doubles. MTBF HDD1 + MTBF HDD2 + MTBF of the controller (which could be replaced probably) double the suceptibility to impact ,power event, ect. loss of a single drive means the whole array is gone
It should be transient performance space not long term storage, I run HDDs in other redundant arrays or as singles for several months, so that any issues that may have occured in handling or shipping have time to develop before I trust it to a RAID 0, if they havent developed by then with care they shouldnt (good environment, proper handling)
If you do employ a RAID0 as storage, get very serious about backup, also, its not so easy to image RAID arrays, there is no official support for doing it with Ghost or Drive Image, sometimes it does work however
In short the size of the stripe greatly depends on your typical access pattern, a large stripe is ideal for working with say large video files, smaller stripe sizes will benchamrk better
some more stripe size info
http://www.storagereview.com/php/tiki/tiki-pagehistory.php?page=StripeSize&diff2=2
you should also read the "As the disc spins" series, linked to at the top of the board (Sticky thread)
the above stripe size issues apply to RAID0, in a RAID5, it impacts reads more than writes, because of the parity calculations, also you need to factor in the cache size (on card) the controller has available.
Again Id ask what you application is going to be, there is an exciting hybrid RAID 3 development on the horizon (havent found a card for sale yet, but they are getting reviewed already)
my XS6000 has a dedicated RISC processor just for XOR calculations and it doesnt impact my CPU much if at all, on the otherhand if its software RAID 5 it can be quite alot, (so much so that you might consider a Linux RAID5 which I here is more effecient, cnat confirm)
regarding stripe size, youd typically try to match to your access
so if your dealing with large files (video graphics ect) you employ larger stripes, if its lots of small access then smaller stripes, benchmarks are almost universally biased to the smaller stripes.
Im just going to cut and paste another thread here
-------------------------------------------------------------------
1.) How would I determine the best stripe size? I heard you can choose between good write performance on a sliding scale depending on the stripe size. If possible, id like a balance between the two like below.
Read ----------|---------- Write
Stripe Size
the read vs write balance isnt controlled by the stripe size per se, that involves caches, the controller, the size of the access, and the stripe.
2.) How does the stripe size relate to the cluster size?
same link as above
3.) FAT32's file size limit is 4GB, if I had 2 drives on RAID 0, would the max filesize be 8GB (is it 4GB limit per disk or 4GB limit overall?)
No, the OS see the array as a single HDD, and its a filesystem limit anyway (you should be using NTFS without some other truely compelling reason anyway.)
4.) How do you go on about formatting, partitioning and defragging a RAID 0 set? Is it just the same as you would with 1 drive?
Yes, however making an array bootable is more complex, typically you have to set it bootable in the RAID's BIOS and when installing the OS you will be prompted to load additional SCSI drivers by pressing F6, and then you load the RAID driver (which is SCSI)
5.) I think the defauly cluster size for NTFS in XP Home is 4kb, would the stripe size be best as a multiple of 4?
The default cluster size is dependent on the size of the partition you can manually set a cluster size when you partition
6.) If the cluster size if 4kb and the stripe was set to 2kb for example, would I waste a ton of space? (I noticed that smaller cluster size is more efficient storage, probably because of part filled clusters)
refer to above
7.) Is RAID really unreliable? I hear a few stories that put me off a bit, but it's something I want to try for myself.
Small problems can become big, the potential to loose data more than doubles. MTBF HDD1 + MTBF HDD2 + MTBF of the controller (which could be replaced probably) double the suceptibility to impact ,power event, ect. loss of a single drive means the whole array is gone
It should be transient performance space not long term storage, I run HDDs in other redundant arrays or as singles for several months, so that any issues that may have occured in handling or shipping have time to develop before I trust it to a RAID 0, if they havent developed by then with care they shouldnt (good environment, proper handling)
If you do employ a RAID0 as storage, get very serious about backup, also, its not so easy to image RAID arrays, there is no official support for doing it with Ghost or Drive Image, sometimes it does work however
In short the size of the stripe greatly depends on your typical access pattern, a large stripe is ideal for working with say large video files, smaller stripe sizes will benchamrk better
some more stripe size info
http://www.storagereview.com/php/tiki/tiki-pagehistory.php?page=StripeSize&diff2=2
STR= Sustained Transfer Rate
you should also read the "As the disc spins" series, linked to at the top of the board (Sticky thread)
the above stripe size issues apply to RAID0, in a RAID5, it impacts reads more than writes, because of the parity calculations, also you need to factor in the cache size (on card) the controller has available.
Again Id ask what you application is going to be, there is an exciting hybrid RAID 3 development on the horizon (havent found a card for sale yet, but they are getting reviewed already)
DJDishwateR
Gawd
- Joined
- Jul 12, 2003
- Messages
- 633
My application would be semi long term storage of media mostly. As for the cache size of the RAID controller I cant really tell you cuz its onboard so I assume it using part of the system ram? I'm looking at about 500 GB of storage, should last me 2 years or so. The main reason I want to do RAID 5 is because of its obvious advantages and the accesibility to everyone on my network.