Date: Fri, 27 Mar 2015 10:25:05 +1030 From: "O'Connor, Daniel" <darius@dons.net.au> To: d@delphij.net Cc: freebsd-hackers@freebsd.org, Wojciech Puchar <wojtek@puchar.net> Subject: Re: Seagate Archive HDD Message-ID: <4F65B315-5FFE-4184-91FD-C05A40E0A26E@dons.net.au> In-Reply-To: <55148E42.80708@delphij.net> References: <alpine.BSF.2.20.1503261124380.1417@laptop.wojtek.intra> <55148E42.80708@delphij.net>
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> On 27 Mar 2015, at 09:24, Xin Li <delphij@delphij.net> wrote: > On 03/26/15 03:26, Wojciech Puchar wrote: >> http://www.storagereview.com/seagate_archive_hdd_review_8tb >>=20 >> i want to buy 2 such drives for backup server. >>=20 >> This drives use shingled recording. >>=20 >> Are anyone using them and can confirm they are compatible on >> software level with other disks? I understand average random write >> time would be 5-10 times slower than normal drive because of the >> need of rewrite few full tracks worth of data, but otherwise will >> then be compatible and can i use it as usual? >=20 > My understanding is that the SMR drives are actually different class > of storage device. >=20 > 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/a= ghayev 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) It also has a log section which it writes to and then back fills into = the shingled area later. The upshot is that you get very weird latencies, but generally writing = sequentially is OK. Random read is OK, random write is utterly abysmal = (duh). One thing I would like to know is if the drive supports TRIM so it can = avoid rewriting a band or not. -- Daniel O'Connor "The nice thing about standards is that there are so many of them to choose from." -- Andrew Tanenbaum GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C
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