Date: Thu, 14 May 1998 08:40:39 -0700 From: "Donald E. Lyon, Jr. Ph.D." <DELyonJr@mci2000.com> To: freebsd-questions@FreeBSD.ORG Subject: FW: RAID Message-ID: <000301bd7f4e$a5579900$01c7c7c7@msoft>
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-----Original Message----- From: Donald E. Lyon, Jr. Ph.D. [mailto:DELyonJr@mci2000.com] Sent: Wednesday, May 13, 1998 7:45 PM To: Greg Lehey Subject: RE: RAID Greg, 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. 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. Don > -----Original Message----- > From: Greg Lehey [mailto:grog@lemis.com] > Sent: Monday, May 11, 1998 4:53 PM > To: Doug White; Donald E. Lyon, Jr. Ph.D. > Cc: freebsd-questions@freebsd.org > Subject: Re: RAID > > > 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? > > Greg > -- > See complete headers for address and phone numbers > finger grog@lemis.com for PGP public key > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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