Date: Thu, 26 Mar 2015 17:15:47 -0700 From: Xin Li <delphij@delphij.net> To: "O'Connor, Daniel" <darius@dons.net.au>, d@delphij.net Cc: freebsd-hackers@freebsd.org, Wojciech Puchar <wojtek@puchar.net> Subject: Re: Seagate Archive HDD Message-ID: <5514A133.8060409@delphij.net> In-Reply-To: <4F65B315-5FFE-4184-91FD-C05A40E0A26E@dons.net.au> References: <alpine.BSF.2.20.1503261124380.1417@laptop.wojtek.intra> <55148E42.80708@delphij.net> <4F65B315-5FFE-4184-91FD-C05A40E0A26E@dons.net.au>
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 On 03/26/15 16:55, O'Connor, Daniel wrote: >> On 27 Mar 2015, at 09:24, Xin Li <delphij@delphij.net> wrote: The >> "drive managed" drives as shipped now tries to emulate normal >> hard drive's behavior but they present unique risks: for >> instance, a rewrite of a small block may end up in a >> read-modify-write of a much larger area, so we must refrain from >> doing such operations for critical file system data structure, >> probably by reorganizing the on-disk format to satisfy the need. > > I don't think this is necessarily true - I watched a very > informative presentation about SMR drives - > https://www.usenix.org/conference/fast15/technical-sessions/presentation/aghayev > > The drive has many regions with guard bands so it doesn't have to > rewrite the entire disk for certain writes (it may have to rewrite > a whole band though) That really depends on whether we can afford to lose the whole band of (meta)data. File systems guard against loss of critical data structure by storing replicas of the data in distant places, but these may not have been distant enough to survive band sized loss, or let's say loss of a few cylinders. That's is why I am not that optimistic about what we do nowadays, we would need to revisit the on-disk formats with the new drives and see if adjustments would be necessary. Cheers, - -- Xin LI <delphij@delphij.net> https://www.delphij.net/ FreeBSD - The Power to Serve! Live free or die -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.1.2 (FreeBSD) iQIcBAEBCgAGBQJVFKEwAAoJEJW2GBstM+nsMtIP/j0I4w1gHhKoE6cFSLXZBwgF LosPyr3w3m1NbkFkmOsibqactliuDOUmxKD4OkGnYED6QFW3Xs0S4xuDcjKfbMDy hT4H8e3HEn8AV7DlzCdMUDtKs2zTHTnfiUxfYHfGeYaK2Vr6HZD2oMUgnzJXEKms SbTxrbY1GCHgrlDqlA6ThHToxKT/KQxCDVYdYnLKnUaj+ZdYU42iPiWIx7RWTpQJ ti8xd0Q1gZ2u2/xcVJ6mJMKGASEkQP3yVp/oplkuFqhS+GSePfvoKLaPU2VOpZCU 4RZ2/fF8zGa1OhcgSRPbSTbKKHN1TRwM847uPDeL9i/G82K1ju+7kG9E92lKFUTE p2WXhM6eqVbPx6ZTWtthB9hVlJzJkOekLbCwjgy2ShWLDmtJ2MGsmqha6nWudj26 4V5HEtEmgYPhJ+MdvnqdqcHut82AtNvbLoH9p1IFwKLhqaE+wRA4aqNjBauZRSZ+ Tg8GoR1IURHGmoKM2NVDuwWJujcJTO5bqRm1IPwZSRrBcxrULnmO3o/pmxwnSJhS gpYVAPNLhtCHrUHRKGxnJ+0upPko2h+JV0nZYvbgf4FVk79JnDEKbUQeIVljk4VP mvyTLKCOxGWswZkLGCX2I7pMvrJEXbfxCnHRvPg+LFFJow1VLOFQDzdiQOS6zdS7 lN1g5HJyAQ9gFH2rAN1e =p51q -----END PGP SIGNATURE-----
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