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It's less cost effective to buy many smaller HDDs, but it's probably better for long-term data retention How so? Is the MTBF for a size 2*x drive more than twi
by gcp 10y ago
It's less cost effective to buy many smaller HDDs, but it's probably better for long-term data retention
How so? Is the MTBF for a size 2*x drive more than twice as high as that of a size x drive?
- alex_anglin 10y agoRAID?
- CyberDildonics 10y agoRAID what? You trade redundancy for less space.
- problems 10y agoIf your concern is space, use RAID5 or RAID6, which offer single or dual disk recovery. There's been some concern raised, particularly about errors on RAID5 recovery - the large disk sizes may make a failure during recovery more likely, but in my experience drives more often than not fail completely and totally, all at once or close to it. If you're extra worried about recovery though, my friend has a good setup where he keeps 1 TB RAID1 across all of his 4x8TB drives for personal files and uses the rest in RAID5 for media storage.
- snuxoll 10y agoWhen you are looking at the potential of losing TB's of data it's money well spent. I ponied up some extra money to set my FreeNAS box at home up with a pool of mirrored devices because I care about my data - if you don't then feel free to save the money. (One of these days I'm going to pony up for a LTO drive to do a monthly backup and drop it in a safe deposit box, one ~$115 LTO-7 tape is enough to backup my entire storage array).
- sigstoat 10y ago> One of these days I'm going to pony up for a LTO drive to do a monthly backup and drop it in a safe deposit box, one ~$115 LTO-7 tape is enough to backup my entire storage array the cost of the LTO-7 drive would buy you an eSATA dock and a decent pile of 8TB SMR drives, which you could just write the zfs dump to linearly.
- Alupis 10y agoData stored on tapes is a lot more stable than data on spinning disks, even when sitting on a shelf. I certainly would not replace a tape backup with spinning disk backups - rather, I would use the disks for routine backups and tapes for quarterly archives or similar. Although, for some of our systems, we use rotated tapes nightly. There's a good reason so many folks still use tapes for important systems.
- CyberDildonics 10y agoRAID and smaller disks doesn't somehow change the dynamic of $/TB.
- snuxoll 10y agoIt does, unless you're only factoring in the cost of the drives themselves and not: 1. The power to run them, and the additional cooling and acoustic concerns as a result 2. The cost of extra storage enclosures to support them 3. The additional space used by the smaller drives (do you want 2U of 12x8TB drives, or 4U of 24x4TB drives).
- gcp 10y agoSo RAID two big drives? What's the point?
- minikites 10y agoIn the case of RAID-1, redundancy? The R in RAID?
- gcp 10y agoYes but that doesn't resolve the small vs big drive issue. You can RAID them both. The question wasn't what the point was of RAID, the question was what the point was of smaller drives.
- jasonjayr 10y agoWe are at the point where drives are large enough, that rebuilding an array of large drives have a dangerously high probability that it will cause another failure in another drive, killing the array.
- mdorazio 10y agoI don't think we should really be looking at drive MTBF, but rather some measure of total expected loss. The bigger your drive, the more catastrophic the loss in the event of a failure, so even if the MTBF of a 2x capacity drive is only slightly higher, your total risk is more than 2x as high.
- lallysingh 10y agoOnly if you don't have backups. If you do have backups, the cost of loss is proportional to your I/O rate for time spent in recovery.
- mdorazio 10y agoHence the suggestion of RAID elsewhere in this thread, which means you might as well get more smaller drives in an array since the $/TB seems not to be dropping on these bigger drives.
- epistasis 10y agoRAID is a really bad idea with larger disks, as 1)not all sources of failure are uncorrelated 2) with huge disks, the rebuild time to replace that failed disk gets really really long (I would guess 2-3 days to fully write to one of these disks. Edit: rebuilding a RAID rather than writing straight will take several times longer.) 3) during rebuild all the disks are taxed quite heavily, especially if they are still performing their typical day to day IO. The larger the disk, the more of them you want in a non-RAID unified erasure coded pool in order to manage these failures more gracefully.
- lmm 10y agoI just rebuilt a raidz2 (4x4TB disks) on my home "server". Took a couple of days. I've never had even a single disk fail during rebuilding to date, so I'm not super worried about the risk of having 2x failures during the 4 days or so it takes to replace a disk (next-day delivery on the replacement and then doing the rebuild). It's a lot more "just works" than backups would be - in principle I'm not worried about high availability as such, but I am worried about faff when replacing.