On Monday 10 March 2014 17:02:10 Chris Hoogendyk did opine: > 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.
The dependability of the SSD in the face of being filled to a high percentage of their capacity, plus the offline time where they hold the writes as they do "wear leveling" and then emptied again each day, will likely use up the spare sectors rapidly, 2 such SSD's would likely not be 100% trouble-free by the time they've been in service a year. By and large, my guess would be that a 5 pack of commodity terrabyte drives would be the more dependable of the two once the drives firmware has been brought up to date, and certainly cheaper since the commodity terrabyte drives are now around $70/copy with a seagate label on them. But do expect to have to visit the Seagate site, find that drives latest firmware, put in on a cd and reboot to it and let that firmware update them all if they are from the same production run. My 4 have been bullet proof for about 3.5-4 years now. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene>
