Thanks for the links, Chris. Very interesting info indeed!
I was basing my longevity concerns from the spec: http://ocz.com/consumer/vector-150-ssd/specifications of a very high performance consumer SSD. But these are consumer SSD's for sure (with MLC memory). Not enterprise grade or SLC. Regardless, at the link above, the spec says "Endurance: Rated for 50GB/day of host writes for 5 years under typical client workloads". To me, the implication is that writing more than 50 GB per day could shorten the life below 5 years. In an application where it is used as a staging disk for Amanda, _might_ your systems write much _more_ than 50GB per day, if your site were big enough to warrant use of an LTO tape in the first place? Anyway, we do not have any experience with SSD's in this kind of scenario. Yes, we do have some large EMC storage systems for our Oracle databases connected to our Sun servers via optical fiber, where there are indeed some SSD's used for intermediate storage before the read/write to the main hard disk drives. But, the systems are too new (less than a year old) for any kind of assessment of SSD life at this point. Z -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Chris Hoogendyk Sent: Tuesday, March 11, 2014 2:04 PM To: AMANDA users Subject: Re: followup on recommendations for tape libraries I've had a couple of responses talking about the potentially short lifetime of SSDs based on how much is written to them. I have some comments on that, some links, and am still interested if anyone has any first hand experience with the scenario we are considering. First off, we expect to be looking at server class SSD devices, probably SLC based, but we haven't gotten specs on what options and prices we have with Supermicro yet. I would note that Sun/Oracle have for several years been configuring data storage systems with SSDs for the write-intent-logs for ZFS filesystems. It is fairly routine to spec a Sun/Oracle storage system with a fair number of SSDs alongside a large number of HDDs, all of them server class devices. The write-intent-log is the highest usage component of the storage system, and they wouldn't be using SSDs there if they were routinely failing in a year or two. This link is one of the better ones explaining calculations, usage scenarios, and life spans for SSDs: http://hblok.net/blog/posts/2013/03/03/concerns-about-ssd-reliability-debunked-again/ The above was based on work in the link in this one: http://beta.slashdot.org/story/182227 Some interesting comments, one from someone who cycled SLC NAND well over a million cycles without failure. This link from Toshiba is with regard to their consumer brand, but their comments on SSD Myth 5 also mention enterprise SSDs: http://www.toshiba.com/taec/news/media_resources/docs/SSDmyths.pdf Finally, for actual experimental data, these guys took a bunch of consumer grade SSDs and hammered them: http://techreport.com/review/24841/introducing-the-ssd-endurance-experiment They stood up pretty well, and that's consumer grade devices. So, I'm still interested in whether anyone has any real life experiences with SSDs as holding disks for Amanda. Would a pair work well and allow Amanda to drive an LTO6 (up to 160MB/s) in streaming mode somewhere near its rated speed? Also still open as a question is whether Amanda can stage backups to larger holding disk drives, and, when complete, move them to the SSD holding drives before writing them from there to the LTO6 tape. TIA Chris Hoogendyk On 3/10/14 6:20 PM, Syed Zaeem Hosain ([email protected]) wrote: > 1. Continuous writing-reading-deleting to an SDD will wear them out _way_ > faster than you might like - these drives tend to be rated in > "so-many-GBytes-per-day" to get their typical rated life of 5 years or so. > That could be an expensive "solution" too quickly. Although, I do see > performance that is generally two to three times faster than SATA III disk > drives write speeds (non-RAID) for the tests I have done. > > 2. I think that using four large (2 to 4 TB) drives in RAID 0 (or RAID 10 if > you want drive reliability ... don't use RAID 5 since that will have parity > calculation performance hits) will get the performance you need. If the > drives are in a server (rather than an external USB3 or Thunderbolt box like > a Drobo or Synology). You should be able to sustain 200 to 400 MBytes/sec > such a to the RAID pretty readily, I'd think! > > 3. If you still plan on using SSD, OCZ Technology makes PCI Express SSD's > that run much faster than the typical SATA III interfaces (see > http://ocz.com/enterprise for info). But, the cost is high. > > 4. Finally, don't RAID your SSD drives - this usually disables TRIM support > in the drive, as I recall. > > Z > > P.S.: What is the streaming rate of the LTO you are acquiring? What is the > model, etc.? I am wondering what the next gen of tape is now starting to be > available and have not looked yet ... > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Chris Hoogendyk > Sent: Monday, March 10, 2014 1:48 PM > To: AMANDA users > Subject: followup on recommendations for tape libraries > > One issue that comes up repeatedly is the requirements of a server and the > holding disk configuration to keep an LTO6 (or LTO5) streaming at something > approaching its rated speed, which is faster than that of an individual disk > drive. > > The most common approach is to have an array of high speed disk drives > configured in raid10 or raid5 for holding space to get data transfer speeds > high enough. > > We are trying to set up a new server and a new tape library without breaking > the budget, and we need a lot of external storage just for storage, even > without the question of Amanda and a holding disk. > We have a J4500 hanging off our T5220 and hope to carry it over to a new > Supermicro server. We planned on filling the internal bays on the Supermicro > and using software raid to configure them. > We'll be using Ubuntu LTS, I'm guessing 14.04, since this project will be for > the summer. > > Kicking ideas around for speed, throughput, etc. to drive the LTO, we came up > with the idea of just getting a pair of SSDs for holding disk space. Those > ought to be individually faster than the LTO by a good bit. > > Has anyone done this? Any comments? > > This also lead us to the question/idea of whether Amanda could be configured > with some sort of "staged" holding disk. In other words, suppose you had some > multi-TB disk drives for holding disk, and a couple of SSDs for transfer to > tape. Backups would go to the first stage disk drives. When they were > complete, they would be transferred to the SSDs. The tape would be written > from backups that are complete and on the SSDs. If the tape were out of order > or offline, then the disk drives would provide some capacity for holding > incrementals for a while, whereas if our holding disks were just SSDs, then > our fall back capacity would be substantially smaller. > > Thoughts? > > Might there be a way within Ubuntu of configuring a disk drive with an ssd > for read/write cache that would achieve what we are after? ZFS does something > a bit like this, though not exactly. > > -- --------------- Chris Hoogendyk - O__ ---- Systems Administrator c/ /'_ --- Biology & Geology Departments (*) \(*) -- 347 Morrill Science Center ~~~~~~~~~~ - University of Massachusetts, Amherst <[email protected]> --------------- Erdös 4
