3 ms·

This is definitely right in my area of expertise :) It largely depends upon how frequently you use the data and what is your preferred access time. It's possib

by wazoox 16y ago

This is definitely right in my area of expertise :) It largely depends upon how frequently you use the data and what is your preferred access time. It's possible to build RAID arrays with 2 TB drives (the sweet post right now in price/capacity), or 1 TB 2.5" drives. With a RAID controller that knows how to spin down idle arrays, it can be pretty cheap, let's see : -using 2 TB 3.5" drives in 24 disks arrays, you need 1 24 disks supermicro-based server (21 usable disks) + 3 45 drives supermicro JBODs gives you 240 TB of usable capacity. Two similar systems will give you 480 TB in 8*4 =32U of rack. The setup will draw about 8KW of power when running and weigh about 300 Kg. If you'd rather go with 2.5" drives, 1 24 slots supermicro server chassis + 3 88 slots supermicro JBODs will give you 260 TB of usable capacity. Two systems will give you 520 TB in 28U, draw about 3.5KW and weigh 200 Kg. So I'd definitely go for the 2.5" version. Furthermore, the 2.5" drives stand much better being put to rest quite often. Please note that this volume is also largely in the realm of tape archive. Current tape libraries are fast, and LTO-5 are 1.5TB uncompressed. It can definitely be cheaper in the long run. Caveat lector! this is a quick and dirty, back of the napkin calculation. I'm on my way to install a 96 TB machine at some customer's premises, I've just quickly thrown the numbers together before leaving.

illumin8 16y ago
I would caution against this. If you need the data to truly be protected, don't build it yourself. Here are some questions and issues that can come up: * Using desktop drives, when 24 are mounted in a single chassis, the vibration from those drives will cause a higher rate of failure. Desktop drives were not designed for this purpose and are not made to handle the vibration and heat created by 23 other drives in the same chassis. * When a single drive in your 24 drive chassis fails, how do you know which one it is? On an enterprise storage array, you have the ability to flash an LED so you know which drive to replace, or you have a direct mapping (shelf 2, bay 16) in the error message. If you built it yourself, how do you know which physical drive is /dev/sdzg? * Purchasing a large number of drives from the same batch means they are very likely to start failing around the same date. Can you handle a double disk failure without losing data? How about a triple disk failure? Do you have hot spares capability? * Are you scrubbing your data regularly to make sure those blocks on disk aren't getting silently corrupted over time? If you never read your data or scrub your entire disk regularly, the only time you'll find out if you've lost data is during a RAID rebuild, when you'll get read errors and have complete data loss (unable to read parity from another drive, double disk failure, complete loss of RAID). * Are you able to use RAID 6 or additional parity disk technology to protect against double disk failures? What if I want 3 parity disks to prevent against a triple disk failure? All of these considerations are things that will come up when you're designing a storage system. These are things that enterprise storage vendors spend months with engineers designing. Failure modes should be considered. In my experience with hand built PC server storage arrays, the time you are most likely to lose data is when you have a disk failure, and are rebuilding parity from another disk. If you have many disks from the same batch, a rebuild can stress the disks more than normal, and cause a second disk to fail. This is why RAID 6 is becoming more and more popular. I would caution you to consider that cheap hand built storage usually ends up expensive in the long run, especially when you lose data that you thought was protected.
- wazoox 16y ago
  > don't build it yourself. Of course not. I've built several petabytes worth of storage systems in the past 15 years, OTOH. > Using desktop drives, when 24 are mounted in a single chassis, the vibration from those drives will cause a higher rate of failure. Absolutely. However this is not always directly applicable to all desktop drives. In fact I'm going to reveal a secret : physically, desktop SATA drives are exactly the same as professional grade 24/24h operation-guaranteed SATA drives. When they fall off the assembly line, they're tested for reliability and performance. Over a certain threshold, a drive is deemed professional and receive the pro firmware; under the bar, it's a desktop drive. What is the most important difference between the desktop vs pro firmware? The desktop drive is supposed to be used alone. In case of an error, it will retry, retry and retry again endlessly to ecc-correct the error. OTOH, the pro drives "knows" it's part of a RAID array; at the slightest fault, it will simply cry "I'm failed" and give up. So in case of a transient error, your IOs won't be blocked. There are some other differences depending upon the maker: for instance all Hitachi GST drives carry an accelerometer, but the desktop drive firmware don't know how to use it to compensate for low-frequency vibrations. WD desktop drives have particular settings that make them extremely dangerous to use in RAID arrays. Note that the "pro/consumer" threshold can be moved to reach some volume threshold regardless of the actual drive quality. This happened, I've been bitten. Anyway, prefer the pro drives even if there 50% more expensive. It will save you some headaches. > When a single drive in your 24 drive chassis fails, how do you know which one it is? First, I suppose the maker (in my case, my team), carefully checked that all drives are properly labeled (so that drive 1 is labeled 1, etc); second, decent RAID controllers can flash a drive LED (Adaptec 5xx5 or 6xx5 series come to mind). > Can you handle a double disk failure without losing data? With drives of 1 TB or more, RAID-5 is definitely out and has been so for several years. RAID-6, RAID-6, RAID-6 is the way to go. > These are things that enterprise storage vendors spend months with engineers designing. E-xact-ly. BTW I'm an enterprise storage vendor. However I'm really too far from Louisville to be able to ship there and support it. I just mentioned what is possible; don't forget that nowadays, when you're buying an SGI (or many other big names) storage system you're buying Supermicro hardware.
  - originalgeek 16y ago
beagle3 16y ago
> Please note that this volume is also largely in the realm of tape archive. Current tape libraries are fast, and LTO-5 are 1.5TB uncompressed. It can definitely be cheaper in the long run. A backblaze setup with today's disk costs is <$40K for hardware (for random access!). Even if you don't need quick or random access - how can a tape library compete with that, short or long run, when the ceapest LTOs are at $40/TB (just like disks), tape devices are expensive, robots are expensive, etc? Also, disk prices keep falling, whereas tapes (for the same technology) tend to remain the same price, so if you're considering future growth, disks win again. And furthermore, I have two 15GB hard disks from '99 that I took out of a computer in '2002, and I can still read (tested last month when I was cleaning up; I know the oil might congeal, but it hasn't in this case). I connected them to an external USB-to-IDE converter I found for $10, and they are still available. I also have a tape backup of some kind from the same era - and no way on earth to read it, because I don't have the tape device, and they're no longer being manufactured.

by wazoox 16y ago

illumin8 16y ago

I would caution against this. If you need the data to truly be protected, don't build it yourself. Here are some questions and issues that can come up: * Using desktop drives, when 24 are mounted in a single chassis, the vibration from those drives will cause a higher rate of failure. Desktop drives were not designed for this purpose and are not made to handle the vibration and heat created by 23 other drives in the same chassis. * When a single drive in your 24 drive chassis fails, how do you know which one it is? On an enterprise storage array, you have the ability to flash an LED so you know which drive to replace, or you have a direct mapping (shelf 2, bay 16) in the error message. If you built it yourself, how do you know which physical drive is /dev/sdzg? * Purchasing a large number of drives from the same batch means they are very likely to start failing around the same date. Can you handle a double disk failure without losing data? How about a triple disk failure? Do you have hot spares capability? * Are you scrubbing your data regularly to make sure those blocks on disk aren't getting silently corrupted over time? If you never read your data or scrub your entire disk regularly, the only time you'll find out if you've lost data is during a RAID rebuild, when you'll get read errors and have complete data loss (unable to read parity from another drive, double disk failure, complete loss of RAID). * Are you able to use RAID 6 or additional parity disk technology to protect against double disk failures? What if I want 3 parity disks to prevent against a triple disk failure? All of these considerations are things that will come up when you're designing a storage system. These are things that enterprise storage vendors spend months with engineers designing. Failure modes should be considered. In my experience with hand built PC server storage arrays, the time you are most likely to lose data is when you have a disk failure, and are rebuilding parity from another disk. If you have many disks from the same batch, a rebuild can stress the disks more than normal, and cause a second disk to fail. This is why RAID 6 is becoming more and more popular. I would caution you to consider that cheap hand built storage usually ends up expensive in the long run, especially when you lose data that you thought was protected.

wazoox 16y ago
> don't build it yourself. Of course not. I've built several petabytes worth of storage systems in the past 15 years, OTOH. > Using desktop drives, when 24 are mounted in a single chassis, the vibration from those drives will cause a higher rate of failure. Absolutely. However this is not always directly applicable to all desktop drives. In fact I'm going to reveal a secret : physically, desktop SATA drives are exactly the same as professional grade 24/24h operation-guaranteed SATA drives. When they fall off the assembly line, they're tested for reliability and performance. Over a certain threshold, a drive is deemed professional and receive the pro firmware; under the bar, it's a desktop drive. What is the most important difference between the desktop vs pro firmware? The desktop drive is supposed to be used alone. In case of an error, it will retry, retry and retry again endlessly to ecc-correct the error. OTOH, the pro drives "knows" it's part of a RAID array; at the slightest fault, it will simply cry "I'm failed" and give up. So in case of a transient error, your IOs won't be blocked. There are some other differences depending upon the maker: for instance all Hitachi GST drives carry an accelerometer, but the desktop drive firmware don't know how to use it to compensate for low-frequency vibrations. WD desktop drives have particular settings that make them extremely dangerous to use in RAID arrays. Note that the "pro/consumer" threshold can be moved to reach some volume threshold regardless of the actual drive quality. This happened, I've been bitten. Anyway, prefer the pro drives even if there 50% more expensive. It will save you some headaches. > When a single drive in your 24 drive chassis fails, how do you know which one it is? First, I suppose the maker (in my case, my team), carefully checked that all drives are properly labeled (so that drive 1 is labeled 1, etc); second, decent RAID controllers can flash a drive LED (Adaptec 5xx5 or 6xx5 series come to mind). > Can you handle a double disk failure without losing data? With drives of 1 TB or more, RAID-5 is definitely out and has been so for several years. RAID-6, RAID-6, RAID-6 is the way to go. > These are things that enterprise storage vendors spend months with engineers designing. E-xact-ly. BTW I'm an enterprise storage vendor. However I'm really too far from Louisville to be able to ship there and support it. I just mentioned what is possible; don't forget that nowadays, when you're buying an SGI (or many other big names) storage system you're buying Supermicro hardware.
- originalgeek 16y ago

beagle3 16y ago

> Please note that this volume is also largely in the realm of tape archive. Current tape libraries are fast, and LTO-5 are 1.5TB uncompressed. It can definitely be cheaper in the long run. A backblaze setup with today's disk costs is <$40K for hardware (for random access!). Even if you don't need quick or random access - how can a tape library compete with that, short or long run, when the ceapest LTOs are at $40/TB (just like disks), tape devices are expensive, robots are expensive, etc? Also, disk prices keep falling, whereas tapes (for the same technology) tend to remain the same price, so if you're considering future growth, disks win again. And furthermore, I have two 15GB hard disks from '99 that I took out of a computer in '2002, and I can still read (tested last month when I was cleaning up; I know the oil might congeal, but it hasn't in this case). I connected them to an external USB-to-IDE converter I found for $10, and they are still available. I also have a tape backup of some kind from the same era - and no way on earth to read it, because I don't have the tape device, and they're no longer being manufactured.