SR (SATA+RAID) Appliance Disk Compatibility GuidelinesAlthough Coraid strives to produce storage products that will operate with any standards-conforming disk drive, the fact is that not all drives are readily compatible with our products. Disk compatibility for Coraid storage products means the following:
Currently hard drive vendors supply a variety of drives that work well with Coraid products. There are also many drives that are close enough in specification that modifications to Coraid software could be made that will allow those drives to be used successfully with our products. Going forward, Coraid remains committed to making sure as many of these marginal drives as possible work with our products, but our focus in this guide is to help customers choose drives that are free of quirks and will work well. In general drives marketed under an "Enterprise" or "RAID Class" brand are the ones to choose. As "Enterprise" is just a marketing term, we would like to point out how a customer can determine from a drive's data sheet whether a drive is a suitable candidate. SATA ConformanceThe SATA conformance that we require is really more than just whether or not the disk understands SATA command sequences. The real issue here is whether there are subtle quirks in command ordering or timing that a drive exhibits that end up translating into problems the SR software must handle. Drives designed for operation in a RAID group have techniques to limit the timing quirks as they are programmed to work as a team with other disks under a RAID controller. The data sheet should mention that the drive is designed for RAID applications.Data IntegrityA drive model's data sheet should list a specification for "Non-recoverable Read Error" of at most 1 sector in 1015 bits. Read error rates of 1 sector in 1014 bits or higher are unacceptable. Keep in mind that even though the specified error rates seem very low, drive capacities are very high. Customers using large capacity drives should choose low error rates.Array OperationVendors vary widely in how they report this feature. The data sheet should either advertise a "Rotational Vibration Sensor" or list a tolerance for rotational vibration. Because arrays may stack drives together in one, two, or even three dimensions, the exact amount of rotational vibration that can be tolerated differs by array. The best you can currently do with a data sheet is to make sure that it mentions that the model does something to handle rotational vibration.24x7 OperationOriginally SATA drives were designed with desktop use in mind and assumed that they would only be actively used 20% of the time. While your application may also only exercise the disk 20% of the time which may make a desktop drive seem suitable, please remember that during a RAID recovery the disk will be busy 100% of the time for an extended period of time. Make sure the drive data sheet mentions 24x7 operation and that failure rates specified assume 24x7 operation.If you are a Coraid customer and would like to report about a drive you use, please send email to support@coraid.com including the output of the sos command. Note:Customer support cases regarding drive failure have shown that some hard drive vendors are unwilling to support "desktop" hard drives used in enterprise environments. While we've not yet seen a manufacturer refuse to honor a warranty based on this, we have seen situations where manufacturers were unwilling to debug problems and provide firmware updates to "desktop" hard drive models. Please take this into consideration when purchasing hard drives for the SR Appliance. 1Seagate disks with this reported model have exhibited strange problems. Please see the following Seagate download page for details on updating the drive firmware: http://snurl.com/2tgdj 2The compatibility problem with this disk is only applicable for users of the SR420. This model is not recommended but may work fine with other SR models. 3Customers have reported many problems with drives from this product family. Seagate documentation confirms that all drives with model numbers ending in AS are unsuitable for use in RAID applications such as Coraid products.
For questions/comments, please contact support@coraid.com. |
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