查看完整版本 : SSD 做 Caching 的問題

china2000 2020-5-5 04:30 PM

SSD 做 Caching 的問題

這個是續 RAID 6 或 RAID 10 的問題延續,
就是如果用一隻 480G SSD 做 Caching,
心想如果呢隻SSD 出事!
結果會係整個 VM crash?
定只會使到整個 VM 系統行得慢,
但仍可運作?
中午曾問過 Dell sales,
佢話怕就用 2隻 SSD!


我過佢始終都無答我呢個問題!
但於我未曾用 SSD 做 caching!
在此想請教一下各位先進!

productdesigner 2020-5-5 05:53 PM

caching會延遲將啲cache data寫返入HDD,而系統唔會亦無能力check啲data啱唔啱,所以cache corrupt最後HDD刀corrupt,以下你可以問返sales confirm吓,如果得1隻SSD/NVMe做cache,只係會做read only cache,如果有2隻會變成read/write cache不過force係Raid1,如果有3隻會變成Raid5 cache etc..最多去到Raid6 cache:smile_34::cr_02:smile_o10:

china2000 2020-5-5 09:43 PM

謝productdesigner 兄回覆,
再問過Sales,
問佢點解要多隻 SSSD?
佢解釋話第二隻SSD 係做 RAID 1!
而且隻SSD 係屬於特別型號,
可以應付頻繁讀寫,
但都無正式回覆我個問題!


就係如果SSD 出事後的問題!

productdesigner 2020-5-5 10:02 PM

結論想安全係插1隻SSD做read only cache:smile_34::cr_02:fst_005:

SSD Read/Write Cache Failure led to Volume 1 Crashing
[url=https://www.reddit.com/r/synology/comments/99e132/ssd_readwrite_cache_failure_led_to_volume_1/]https://www.reddit.com/r/synology/comments/99e132/ssd_readwrite_cache_failure_led_to_volume_1/[/url]

朱投炳 2020-5-6 07:37 AM

[quote]原帖由 [i]china2000[/i] 於 2020-5-5 04:30 PM 發表 [url=https://computer.discuss.com.hk/redirect.php?goto=findpost&pid=518206881&ptid=29042078][img]https://computer.discuss.com.hk/images/common/back.gif[/img][/url]
這個是續 RAID 6 或 RAID 10 的問題延續,
就是如果用一隻 480G SSD 做 Caching,
心想如果呢隻SSD 出事!
結果會係整個 VM crash?
定只會使到整個 VM 系統行得慢,
但仍可運作?
中午曾問過 Dell sales,
佢話怕就用 2隻 SSD!


我過佢始終都無答我呢個問題!
但於 ... [/quote]


因為Sales 唔會咁傻去保証你買既SSD唔會壞。壞親佢就會被罷上枱。買兩隻行RAID1 一來保險D死一隻唔會即刻影響你資料使用, 二來又可以令張單價值再高D, 何樂而不為。

china2000 2020-5-7 12:03 AM

個Sales 話明天會同Technical 開一個telephone conference!
到時點我都會同大家回報一下。

abcd5678 2020-5-7 01:54 AM

Last time you mentioned you only has 2 VM. If it is not too big, why not use RAID5/6 SSD as VM or any read/write intensive application like DB. The overall performance would be better and with less concern. Using smaller SSD is much cheaper in long term.

No matter you are using SW or HW RAID, more simple setup is better.

BTW, not all SW and HW cache is equal. Do some search for your setup.

productdesigner 2020-5-7 03:35 PM

依家最頂級原來係Raid7 或者 zfs+Raidz3, 成組array可以同時死3隻:smile_34::cr_02:smile_o10:

[url=https://calomel.org/zfs_raid_speed_capacity.html]https://calomel.org/zfs_raid_speed_capacity.html[/url]
[b]Be Safe, Not Sorry.[/b] When choosing a raid configuration you may look at raidz or RAID5 and see the speed and capacity benefits and decide it is a good choice. From real world experience we highly suggest NOT using raid5. It is simply not safe enough. We recommend using RAID1 mirroring or RAID6 (double parity) or even RAID7 (triple parity). The problem with raid5 is you only have one drive with parity. When one drive dies the raid5 array is degraded and you can not loose another drive before you lose the entire array; i.e. all your data is lost. What happens most of the time is one drive dies, you replace the drive and the array starts resilvering or rebuilding. This is when the other disks are being stressed and during this rebuild is when you have a very good chance (around 8%) that you you will lose another drive. For more information please take some time to read [url=http://storagemojo.com/2007/02/26/netapp-weighs-in-on-disks/]NetApp Weighs In On Disks[/url] which was written in 2007, but is still valid today since drive technology has not changed much.
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查看完整版本: SSD 做 Caching 的問題