> -----Original Message----- > From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid- > owner@xxxxxxxxxxxxxxx] On Behalf Of Johannes Truschnigg > Sent: Saturday, October 30, 2010 3:33 AM > To: Leslie Rhorer > Cc: linux-raid@xxxxxxxxxxxxxxx > Subject: Re: 3T drives and RAID > > Hi Leslie, > > Please note: I don't have any hands-on experience with drives over 2TB > in size, but I'm interested in the subject as well, and so I will reply > with what (I think) I know nonetheless ;) > > On Fri, 29 Oct 2010 22:36:27 -0500 > "Leslie Rhorer" <lrhorer@xxxxxxxxxxx> wrote: > > > WD has finally released a 3T drive employing 4K sectors and > > Advanced Formatting. I have some questions about Linux / RAID > > compatibility. The compatibility chart says using the drive with > > Linux requires employing the included HBA. Is the HBA really > > required if the system will not be booting from the drive? Why? > > I don't think that's really the case. I didn't see how it would be, myself. I can understand how it would be needed in order for the drive to be bootable, since the BIOS can't handle the drive, but I was scratching my head over why it might be required otherwise. I know the ECC and physical layout for drives with 4K sectors is quite different than that of legacy drive formats, but it seemed to me as long as the OS can properly calculate the sector numbers, the controller should be happy. > The real troublemaker for > common SOHO computer setups with drives that big are not the hardware or > the ATA protocol (there's theoretical support for drives as large as 2 > PetaBytes since ATA-6, aka UDMA/100 for EIDE/PATA drives), but simply > MBR partitions. So if your goal isn't booting off of an MBR partition > that's as large as your whole drive (or larger than 2TB, for that > matter), you shouldn't run in any problems. Using advanced partitioning > schemes (like GPT) or LVM on GNU/Linux, for example, should be able to > deal with partition size above 2TB perfectly well. I won't be partitioning, at all. The file system (XFS) is written directly to the raw array, and the array is assembled from raw drives. I have relatively small (500G) drives for booting, partitioned into /, /boot, and swap, but the data is all kept on a single file system formatted on a simple RAID6 volume. > > What is the minimum kernel version required? I am wanting to use > > these on a RAID6 array with no drive partitioning underneath the > > array (raw disks) using md / mdadm. I'm using a pair of PM based > > eSATA RAID enclosures to house the drives, so if I need to replace my > > adapters, the replacements will need to have eSATA ports (at least 4 > > per card) compatible with PM enclosures, which the included HBAs do > > not have. I'm not sure if the little Sil3124 adapters I currently > > have will fill the bill. Performance is not a big issue. > > I don't think you'll run into problems with that kind of setup, either. > Support for SATA Port Multipliers are a matter of the controller and its > driver (check libata docs if your combination is supported - if memory > serves, Sil3xxx _do_ support PMs), and as I said before, the ATA Yes, they do. That's really not the question. I know my Sil3124 adapters support PMs: I'm using them right now. > standard - and therefore, compliant devices - should cope with drives > > 2TB quite well. Your enclosures presumably are dumb devices anyway, > and don't contain any ICs or logic that would interfere with the data on > the link between the HBA's SATA port and your drives. Well, they have Port Multipliers, but the PMs should not care about the drive format. I didn't think the SATA controller would, eitehr, but I wasn't certain. > > In addition, I am going to need to add capacity to my existing > > arrays well before I have the money to replace them completely with 3T > > drives. I'm going to need six 3T drives per array to completely > > replace the 1T and 1.5T drives currently in use. In the mean time, I > > could upgrade the existing arrays with 1T and 1.5T drives, but that > > money would be more or less wasted when the drives are replaced in a > > few months. I would much rather buy a couple of 3T drives and move > > them over to the new array when it gets built. Will there be an > > issue with attempting to add a 4K sector drive to a RAID6 array built > > out of 512 byte sectors? > > I don't think so, since you can treat "Advanced Format" drives as > though as they were 512b sector drives, with the drawback of severly > degraded write performance. With md's common values for chunk-size (64k > and more), you should have no problems like the hugely increased write > penalty you get when incorrectly aligning your writes so they don't > take care of sector boundaries. If you're not using partitions but > whole drives as the building blocks of your array anyway, and your chunk > size is an integer multiple of the drives' 4k sector size, you should be > fine. Md will automatically treat the oddball drive as if it had .5K sectors, or does one need to tell ma (or the kernel) to do so? -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
