[Gluster-users] RAID options for Gluster

[Fernando Frediani (Qube)]

Well, as far as I know the amount of IOPS you can get from a RAID 5/6 is the same that you get from a single disk. The write can not be acknowledged until it is written to all the data and parity disks.

With regards it scaling beyond 16 disks, yeah it might do and be possible to create with more disks, however it might increase the rebuild time when a disk gets replaced and in theory it should decrease performance as there will be more disks to acknowledge writes.

Fernando

From: George Machitidze [mailto:giomac at gmail.com]
Sent: 14 June 2012 14:01
To: Fernando Frediani (Qube)
Cc: gluster-users at gluster.org
Subject: Re: [Gluster-users] RAID options for Gluster

Hi,

Some corrections...
Cons:
Extra cost of the RAID controller.
Performance of the array is equivalent a single disk + RAID controller caching features.
RAID doesn’t scale well beyond ~16 disks

Performance of the array is not equivalent of a single disk and doesn't depend only on cache size or spec. features - it depends on the total IOPS, block sizes, access type etc.

RAID scales well beyond 16 disks, ex. for Adaptec. Yes, it will scale, but is it software or hardware, for both array reconfiguration and grow is the same kind of problem - data needs to be reallocated.

Maximum Number of Arrays that can be created on the same set of drives: 4
Maximum Logical Drive Size: 512TB
Maximum Number of Drives in Striped Array (such as RAID 0): 128
Maximum Number of Drives in RAID 5 Array: 32
Maximum Number of Drives in RAID 50 Array: 32
Maximum Number of Drives in RAID 6 Array: 32
Maximum Number of Drives in RAID 60 Array: 32
Available Stripe Sizes for Arrays are 16, 32, 64, 128, 256, 512, or 1024 KB. Striped RAID configurations have a default stripe size of 256 KB.
Note: A RAID 10, RAID 50, or RAID 60 array cannot have more than 32 legs when created using the Build method. Maximum disk drive count is only limited by RAID level. For instance:
a RAID 10 array built with 32 RAID 1 legs (64 disk drives) is supported
a RAID 50 array built with 32 RAID 5 legs (number of drives will vary) is also supported


Best regards,
George Machitidze


On Thu, Jun 14, 2012 at 3:06 PM, Fernando Frediani (Qube) <fernando.frediani at qubenet.net<mailto:fernando.frediani at qubenet.net>> wrote:
> Cons:
>
> Extra cost of the RAID controller.
>
> Performance of the array is equivalent a single disk + RAID controller
> caching features.
>
> RAID doesn’t scale well beyond ~16 disks
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