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Date:      Fri, 15 May 1998 12:02:19 +0930
From:      Greg Lehey <grog@lemis.com>
To:        "Donald E. Lyon, Jr. Ph.D." <DELyonJr@mci2000.com>, freebsd-questions@FreeBSD.ORG
Subject:   Vinum (was: RAID)
Message-ID:  <19980515120219.K305@freebie.lemis.com>
In-Reply-To: <000301bd7f4e$a5579900$01c7c7c7@msoft>; from Donald E. Lyon, Jr. Ph.D. on Thu, May 14, 1998 at 08:40:39AM -0700
References:  <000301bd7f4e$a5579900$01c7c7c7@msoft>

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On Thu, 14 May 1998 at  8:40:39 -0700, Donald E. Lyon, Jr. Ph.D. wrote:
>
>> From: Greg Lehey [mailto:grog@lemis.com]
>> Sent: Monday, May 11, 1998 4:53 PM
>>
>> On Mon, 11 May 1998 at 14:56:20 -0700, Doug White wrote:
>>> On Mon, 11 May 1998, Donald E. Lyon, Jr. Ph.D. wrote:
>>>
>>>> 1. Does FreeBSD have something like SCO's Virtual Disk Manager (RAID)?
>>>
>>> Although I'm not familiar with that product directly, we do have ccd,
>>> which is disk striping.  That may be supplanted by vinum in the future,
>>> which is much more flexible.
>>
>> I'm the author of vinum.  I don't know about the Virtual Disk Manager,
>> but it could be something similar.  Could you describe it, please?
>
> The SCO Virtual Disk Manager is an add-on, layered product that enhances the
> ability of SCO OpenServer Release 5 to provide flexible configurations of
> high reliability, high performance data storage.

Thanks.  This looks pretty much the same thing as vinum.  I've just
released the first alpha test version, but I don't recommend it to
anybody who isn't prepared for a lot of work in getting it into shape.

Greg

> Virtual disks are used to organize data in multi-disk systems. Areas from
> several discrete hard disks can be assigned to a virtual disk, which is
> accessible as if it were a single physical disk by applications running on
> the system.
>
> Virtual disks can support partitions larger than a single disk's physical
> extent. In addition, virtual disks can be organized so that I/O requests are
> written to an array of disk drives in parallel. This can be used to mirror
> data (providing increased security against hardware failures), or to stripe
> data across multiple disks (improving performance).
>
> There are several virtual disk types: most are implemented as RAID
> (redundant array of inexpensive disks) configurations. In this release, RAID
> configurations 0, 1, 4, 5, 10 and 53 are supported.
>
> Disk "pieces" can be assigned to virtual disks as needed. Some virtual disk
> types can use this facility in the event of a hardware failure. A disk piece
> is brought online from a spare disk drive kept on hot standby, and the lost
> data is regenerated from the parity information and data stored on the other
> drives in the array. This permits an array to keep working at near-optimal
> performance despite isolated hardware failures.
>
> Virtual disks can be administered without taking the system offline,
> including online reconfiguration, online restore, and online data
> verification. This capability reduces disk downtime due to storage system
> reconfiguration and performance tuning.
>
> Virtual disks are used to manage data in a more flexible way on systems with
> multiple hard disks. They are particularly useful for improving the
> performance of large applications, such as databases, by distributing the
> data across multiple disks and speeding up disk I/O.
>
> Units of virtual disk space look like real disk partitions to programs
> running on the system, but their characteristics can be changed dynamically
> using the Virtual Disk Manager.
>
> The Virtual Disk Manager adds an additional level of software control to the
> allocation of data storage. Normally, when applications request some data
> from the filesystem, the kernel uses the filesystem to discover the disk
> blocks where the data is stored and returns the data directly. When a
> virtual disk is in use, the system reads and writes to a virtual disk
> driver, which in turn manages the physical allocation of data across several
> disks.
>
> This has a number of advantages. A virtual disk can be assembled from a
> collection of small disks, or pieces of disks, so that rather than providing
> a set of small partitions they can be used to provide a single large
> contiguous disk space. Data can be duplicated (``mirrored'') across drives,
> so that if one drive succumbs to a hardware failure, the system can continue
> to operate without interruption: by using a technique called ``striping'',
> data can be read from and written to disks in parallel, significantly
> improving I/O performance.
>
> Etc...
>
> This was copied from www.sco.com, Openserver, Virtual Disk Manager pages.
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